High refractive index glass

ABSTRACT

Provided is a high refractive index glass, comprising, as a glass composition in terms of mass %, 0 to 10% of B 2 O 2 , 0.001 to 35% of SrO, 0.001 to 30% of ZrO 2 +TiO 2 , and 0 to 10% of La 2 O 2 +Nb 2 O 5 , having a mass ratio of BaO/SrO of 0 to 40 and a mass ratio of SiO 2 /SrO of 0.1 to 40, and having a refractive index nd of 1.55 to 2.3.

This application claims the benefit of U.S. provisional application No.61/489,833, filed May 25, 2011, the contents of which are incorporatedby reference.

TECHNICAL FIELD

The present invention relates to a high refractive index glass, and morespecifically, to a high refractive index glass suitable for, forexample, an OLED device, in particular, an OLED lighting device.

BACKGROUND ART

In recent years, attention has been increasingly paid to a display and alighting device which use an OLED light-emitting element. Each of theOLED devices has a structure in which an organic light-emitting elementis sandwiched by substrates (glass sheets) on which a transparentconductive film such as an ITO or FTO film is formed (see, for example,Patent Literature 1). When an electric current flows through the organiclight-emitting element in this structure, a hole and an electron in theorganic light-emitting element are combined to emit light. The emittedlight enters a glass sheet via the transparent conductive film and isreleased out while repeating reflection in the glass sheet.

CITATION LIST

Patent Literature 1: JP 2007-149460 A

SUMMARY OF INVENTION Technical Problem

Meanwhile, an organic light-emitting element has a refractive index ndof 1.8 to 1.9, and transparent electrode film has a refractive index ndof 1.9 to 2.0. On the other hand, a glass substrate usually has arefractive index nd of about 1.5. Thus, a conventional OLED deviceinvolves a problem in that a difference in refractive index between theglass substrate and the ITO film at their interface leads to a highreflectance, and hence light emitted from the organic light-emittingelement cannot be extracted efficiently.

When a high refractive index glass is used as a glass sheet, thedifference in the refractive index between the glass sheet and thetransparent electrode film at their interface can be reduced.

An optical glass used for an optical lens and the like is known as ahigh refractive index glass. An optical glass obtained by forming glassinto a droplet glass having a spherical shape by a droplet formingmethod or the like, and press-forming the droplet glass so as to have apredetermined shape while applying heat treatment again to the dropletglass is used for the optical lens and the like. This optical glass hasa high refractive index nd but has a low liquidus viscosity, and hencethe optical glass needs to be formed by, for example, a droplet formingmethod which is performed at a fast cooling rate, becausedenitrification of glass occurs at the time of forming the glass intothe optical glass otherwise. Thus, it is necessary to enhance thedevitrification resistance of the high refractive index glass in orderto solve the above-mentioned problem.

Meanwhile, with a reduction in thickness of an OLED display or the likeand an increase in size thereof, the development of a glass sheet havinga smaller thickness and a larger area has been required. It is necessaryfor producing such glass sheet to form glass into a glass sheet by afloat method or a down-draw method (overflow down-draw method or slotdown-draw method). However, because conventional high refractive indexglass had a low liquidus viscosity, the high refractive index glass wasnot able to be formed into a glass sheet by the float method or thedown-draw method, and hence it was difficult to form the glass into aglass sheet having a reduced thickness and an increased size. Note thatthe development of a glass sheet having a reduced thickness and anincreased size for an OLED lighting device has also been requested.

On the other hand, when oxides, in particular, La₂O₃, Nb₂O₅, and Gd₂O₃,are added in the composition of glass, the refractive index nd of theresultant glass sheet can be increased while the reduction of theliquidus viscosity of the glass is suppressed to a certain extent.However, these rare metal oxides involve a problem in that theirmaterial costs are high. Further, when rare metal oxides are added inthe composition of glass in a large amount, the devitrificationresistance of the glass lowers and it becomes difficult to form theglass into a glass sheet. Note that, when rare metal oxides are added inglass in a large amount, the acid resistance of the glass also lowers.

Thus, a technical object of the present invention is to provide a highrefractive index glass which has a refractive index nd matching to thatof an organic light-emitting element and that of a transparent electrodefilm and has good denitrification resistance even though the content ofrare metal oxides (in particular, La₂O₃, Nb₂O₅, and Gd₂O₃) is small.

Solution to Problem

<First Invention>

The inventors of the present invention have made extensive studies, andhave consequently found that the above-mentioned technical object can beachieved by restricting the content range of each component and therefractive index of the resultant high refractive index glass to eachpredetermined range. The finding is proposed as a first invention. Thatis, a high refractive index glass of the first invention comprises, as aglass composition in terms of mass %, 0 to 10% of B₂O₃, 0.001 to 35% ofSrO, 0.001 to 30% of ZrO₂+TiO₂, and 0 to 10% of La₂O₃+Nb₂O₅, having amass ratio of BaO/SrO of 0 to 40 and a mass ratio of SiO₂/SrO of 0.1 to40, and having a refractive index nd of 1.55 to 2.3. Herein, the“ZrO₂+TiO₂” refers to the total amount of ZrO₂ and TiO₂. The“La₂O₃+Nb₂O₅” refers to the total amount of La₂O₃ and Nb₂O₅. The“refractive index nd” can be measured with a commercially availablerefractometer, and can be measured, for example, by producing sampleshaving a rectangular parallelepiped shape of 25 mm by 25 mm by about 3mm, then subjecting the samples to annealing treatment at a cooling rateof 0.1° C./min in the temperature range from (annealing point Ta+30° C.)to (strain point Ps-50° C.), and subsequently using a refractometerKPR-2000 manufactured by Shimadzu Corporation in a state in which animmersion liquid having a refractive index matching to that of thesamples is immersed between two glass samples. The “annealing point Ta”refers to a value obtained through measurement based on a method asdescribed in ASTM C338-93. The “strain point Ps” refers to a valueobtained through measurement based on a method as described in ASTMC336-71.

Second, the high refractive index glass of the first inventionpreferably has a liquidus viscosity of 10^(3.0) dPa·s or more. Herein,the “liquidus viscosity” refers to a value obtained by measuring theviscosity of glass at its liquidus temperature by a platinum sphere pullup method. The “liquidus temperature” refers to a value obtained bymeasuring a temperature at which crystals of glass deposit after glasspowder that has passed though a standard 30-mesh sieve (500 μm) andremained on a 50-mesh sieve (300 μm) is placed in a platinum boat andkept in a gradient heating furnace for 24 hours.

Third, the high refractive index glass of the first invention preferablyhas a sheet shape. Herein, the term “sheet shape” is not restrictivelyinterpreted, comprises a film shape having a small thickness, such asthe shape of a film-shaped glass arranged along a cylindrical product,and also comprises the shape of a glass sheet having formedirregularities in one surface thereof.

Fourth, the high refractive index glass of the first invention ispreferably formed by a float method.

Fifth, the high refractive index glass of the first invention preferablyhas a temperature at 10⁴ dPa·s of 1,250° C. or less. Herein, the“temperature at 10⁴ dPa·s” refers to a value obtained by measurementusing a platinum sphere pull up method.

Sixth, the high refractive index glass of the first invention preferablyhas a strain point of 650° C. or more.

Seventh, the high refractive index glass of the first invention ispreferably used in a lighting device.

Eighth, the high refractive index glass of the first invention ispreferably used in an OLED lighting device.

Ninth, the high refractive index glass of the first invention ispreferably used in an OLED display.

Tenth, a high refractive index glass of the first invention comprises,as a glass composition in terms of mass %, 0 to 8% of B₂O₃, 0.001 to 35%of SrO, 0 to 12% of ZnO, 0.001 to 30% of ZrO₂+TiO₂, 0 to 5% ofLa₂O₃+Nb₂O₅, and 0 to 10% of Li₂O+Na₂O+K₂O, has a mass ratio of BaO/SrOof 0 to 20, a mass ratio of SiO₂/SrO of 0.1 to 20, and a mass ratio of(MgO+CaO)/SrO of 0 to 20, and has a refractive index nd of 1.58 or more,a liquidus viscosity of 10^(3.5) dPa·s or more, and a strain point of670° C. or more. Herein, the “Li₂O+Na₂O+K₂O” refers to the total amountof Li₂O, Na₂O, and K₂O. The “MgO+CaO” refers to the total amount of MgOand CaO.

Eleventh, a high refractive index glass of the first inventioncomprises, as a glass composition in terms of mass %, 10 to 50% of SiO₂,0 to 8% of B₂O₃, 0 to 10% of CaO, 0.001 to 35% of SrO, 0 to 30% of BaO,0 to 4% of ZnO, 0.001 to 30% of ZrO₂+TiO₂, 0 to 5% of La₂O₃+Nb₂O₅, and 0to 2% of Li₂O+Na₂O+K₂O, has a mass ratio of BaO/SrO of 0 to 20, a massratio of SiO₂/SrO of 1 to 15, and a mass ratio of (MgO+CaO)/SrO of 0 to20, and has a refractive index nd of 1.6 or more, a liquidus viscosityof 10^(4.0) dPa·s or more, and a strain point of 670° C. or more.

Twelfth, a glass sheet for a lighting device of the first inventioncomprises, as a glass composition in terms of mass %, 0.1 to 60% ofSiO₂, 0 to 10% of B₂O₃, 0.001 to 35% of SrO, 0 to 40% of BaO, 0.001 to30% of ZrO₂+TiO₂, and 0 to 10% of La₂O₃+Nb₂O₅, and has a refractiveindex nd of 1.55 to 2.3.

Thirteenth, a glass sheet for an OLED lighting device of the firstinvention comprises, as a glass composition in terms of mass %, 0.1 to60% of SiO₂, 0 to 10% of B₂O₃, 0.001 to 35% of SrO, 0 to 40% of BaO,0.001 to 30% of ZrO₂+TiO₂, and 0 to 10% of La₂O₃+Nb₂O₅, and has arefractive index nd of 1.55 to 2.3.

Fourteenth, a glass sheet for an OLED display of the first inventioncomprises, as a glass composition in terms of mass %, 0.1 to 60% ofSiO₂, 0 to 10% of B₂O₃, 0.001 to 35% of SrO, 0 to 40% of BaO, 0.001 to30% of ZrO₂+TiO₂, and 0 to 10% of La₂O₃+Nb₂O₅, and has a refractiveindex nd of 1.55 to 2.3.

Fifteenth, a high refractive index glass of the first inventioncomprises, as a glass composition in terms of mass %, 35 to 60% of SiO₂,0 to 1.5% of Li₂O+Na₂O+K₂O, 0.1 to 35% of SrO, 0 to 35% of BaO, 0.001 to25% of TiO₂, and 0 to 9% of La₂O₃+Nb₂O₅+Gd₂O₃, and having a refractiveindex nd of 1.55 to 2.3. Herein, the “La₂O₃+Nb₂O₅+Gd₂O₃” refers to thetotal amount of La₂O₃, Nb₂O₅, and Gd₂O₃.

Sixteenth, a high refractive index glass of the first inventioncomprises, as a glass composition in terms of mass %, 35 to 60% of SiO₂,0 to 1.5% of Li₂O+Na₂O+K₂O, 0.1 to 20% of SrO, 17 to 35% of BaO, 0.01 to20% of TiO₂, and 0 to 9% of La₂O₃+Nb₂O₅+Gd₂O₃, and having a refractiveindex nd of 1.55 to 2.3.

Seventeenth, the high refractive index glass of the first inventionpreferably further comprises 0 to 3 mass % of B₂O₃.

Eighteenth, the high refractive index glass of the first inventionpreferably further comprises 0 to 3 mass % of MgO.

Nineteenth, the high refractive index glass of the first inventionpreferably further comprises 1 to 20 mass % of ZrO₂+TiO₂.

Twentieth, the high refractive index glass of the first invention ispreferably formed by a down-draw method. Herein, the “down-draw method”refers to, for example, an overflow down-draw method, a slot down-drawmethod, or a redraw method.

<Second Invention>

The inventors of the present invention have made extensive studies, andhave consequently found that the above-mentioned technical object can beachieved by restricting the composition range of glass to apredetermined range. The finding is proposed as a second invention. Thatis, a high refractive index glass of the second invention comprises, asa glass composition in terms of mass %, 30 to 60% of SiO₂, 0 to 15% ofB₂O₃, 0 to 15% of Al₂O₃, 0 to 10% of Li₂O, 0 to 10% of Na₂O, 0 to 10% ofK₂O, 20 to 60% of MgO+CaO+SrO+BaO+ZnO, 0.0001 to 20% of TiO₂, 0 to 20 ofZrO₂, and 0 to 10% of La₂O₃+Nb₂O₅, and having a mass ratio of BaO/SrO of0 to 40 and amass ratio of SiO₂/SrO of 0.1 to 40, and having arefractive index nd of 1.55 to 2.3. Herein, the “MgO+CaO+SrO+BaO+ZnO”refers to the total amount of MgO, CaO, SrO, BaO, and ZnO. The“La₂O₃+Nb₂O₅” refers to the total amount of La₂O₃ and Nb₂O₅. The“refractive index nd” can be measured with a refractometer, and can bemeasured, for example, by producing samples having a rectangularparallelepiped shape of 25 mm by 25 mm by about 3 mm, then subjectingthe samples to annealing treatment at a cooling rate of 0.1° C./min inthe temperature range from (annealing point Ta+30° C.) to (strain pointPs-50° C.), and subsequently using a refractometer KPR-200 manufacturedby Kalnew Co., Ltd. in a state in which an immersion liquid having arefractive index nd matching to that of the samples is immersed betweentwo glass samples. The “annealing point Ta” refers to a value obtainedthrough measurement based on a method as described in ASTM C338-93. The“strain point Ps” refers to a value obtained through measurement basedon a method as described in ASTM C336-71.

A high refractive index glass of the second invention comprises 30 to60% of SiO₂, 0 to 15% of B₂O₃, 0 to 15% of Al₂O₃, 20 to 60% ofMgO+CaO+SrO+BaO+ZnO, 0.0001 to 20% of TiO₂, and 0 to 20% of ZrO₂. Withthis, the devitrification resistance of the high refractive index glasscan be enhanced while its refractive index nd is increased.

The high refractive index glass of the second invention comprises 0 to10% of La₂O₃+Nb₂O₅. As a result, its material cost can be reduced andits devitrification resistance and acid resistance can be easilyenhanced.

The high refractive index glass of the second invention comprises 0 to10% of Li₂O, 0 to 10% of Na₂O, and 0 to 10% of K₂O. As a result, itsacid resistance improves, and even if these alkali components elute inan etching step with acid, the glass does not easily become cloudy. Notethat, for example, the production process of an OLED display or the likecomprises the etching step with acid, and hence, when a glass sheet haslow acid resistance, the glass sheet is corroded in the etching step andbecomes cloudy. When the glass sheet is cloudy, the transmittance of theglass sheet lowers, resulting in difficulty in producing a displayhaving a high definition.

The high refractive index glass of the second invention has a refractiveindex nd of 1.55 to 2.3. As a result, the high refractive index glasshas a refractive index nd easily matching to that of an organiclight-emitting element and that of a transparent electrode film, andlight emitted from an organic light-emitting element can be extractedout efficiently.

Second, the high refractive index glass of the second inventionpreferably comprises, as a glass composition in terms of mass %, 35 to60% of SiO₂, 0 to 15% of B₂O₃, 0 to 15% of Al₂O₃, 0 to 10% of Li₂O, 0 to10% of Na₂O, 0 to 10% of K₂O, 20 to 60% of MgO+CaO+SrO+BaO+ZnO, 0.0001to 20% of TiO₂, 0.0001 to 20% of ZrO₂, and 0 to 10% of La₂O₃+Nb₂O₅, andhas a refractive index nd of 1.55 to 2.3.

Third, the high refractive index glass of the second inventionpreferably comprises, as a glass composition in terms of mass %, 35 to60% of SiO₂, 0 to 15% of B₂O₃, 0 to 15% of Al₂O₃, 0 to 1% of Li₂O, 0 to1% of Na₂O, 0 to 1% of K₂O, 0 to 1% of Li₂O+Na₂O+K₂O, 20 to 50% ofMgO+CaO+SrO+BaO+ZnO, 0.1 to 35% of BaO, 0.0001 to 20% of TiO₂, 0.0001 to20% of ZrO₂, and 0 to 10% of La₂O₃+Nb₂O₅, and has a refractive index ndof 1.55 to 2.3. Herein, the “Li₂O+Na₂O+K₂O” refers to the total amountof Li₂O, Na₂O, and K₂O.

Fourth, the high refractive index glass of the second inventionpreferably comprises 1 mass % or more of B₂O₃.

Fifth, in the high refractive index glass of the second invention thecontent of MgO is preferably 1 mass % or more.

Sixth, the high refractive index glass of the second inventionpreferably has a sheet shape. With this, the high refractive index glassis easily applicable to a substrate for various devices such as an OLEDdisplay, an OLED lighting device, and an organic thin-film solar cell.Herein, the term “sheet shape” is not restrictively interpreted,comprises a film shape having a small thickness, such as the shape of afilm-shaped glass arranged along a cylindrical product, and alsocomprises the shape of a glass sheet having formed irregularities in onesurface thereof.

Seventh, the high refractive index glass of the second inventionpreferably has a liquidus viscosity of 10^(3.0) dPa·s or more. An OLEDlighting device or the like involves a problem in that, when the surfacesmoothness of a glass sheet used therein differs even slightly dependingon parts of its surfaces, the density of an electric current varies atthe time of applying the electric current, causing the unevenness of theintensity of illumination. Further, when the surfaces of a glass sheetare polished to increase its surface smoothness, there occurs a problemin that the processing cost of the glass sheet surges. Thus, when theliquidus viscosity of a high refractive index glass is controlled in theabove-mentioned range, the glass can be easily formed into a glass sheetby an overflow down-draw method or the like, and consequently, a glasssheet having good surface smoothness can be easily manufactured even ifits surfaces are not polished. Herein, the “liquidus viscosity” refersto a value obtained by measuring the viscosity of glass at its liquidustemperature by a platinum sphere pull up method. The “liquidustemperature” refers to a value obtained by measuring a temperature atwhich crystals of glass deposit when glass powder that has passed thougha standard 30-mesh sieve (500 μm) and remained on a 50-mesh sieve (300μm) is placed in a platinum boat and kept in a gradient heating furnacefor 24 hours. The term “overflow down-draw method” refers to a methodcomprising causing molten glass to overflow from both sides of aheat-resistant, trough-shaped structure, and subjecting the overflowingmolten glass to down-draw downward while joining the flows of theoverflowing molten glass at the lower end of the trough-shapedstructure, to thereby form the molten glass into a glass sheet.

Eighth, the high refractive index glass of the second invention ispreferably formed by a float method or a down-draw method. Herein, the“down-draw method” refers to, for example, an overflow down-draw methodor a slot down-draw method.

Ninth, at least one surface of the high refractive index glass of thesecond invention preferably comprises an unpolished surface, theunpolished surface having a surface roughness Ra of 10 Å or less.Herein, the term “surface roughness Ra” refers to a value obtainedthrough measurement by a method in accordance with JIS B0601: 2001.

Advantageous Effects of Invention

According to the first invention and the second invention, it ispossible to provide the high refractive index glass which has arefractive index nd matching to that of an organic light-emittingelement and that of a transparent electrode film and has gooddevitrification resistance while the content of rare metal oxides (inparticular, La₂O₃, Nb₂O₅, and Gd₂O₃) is decreased.

DESCRIPTION OF EMBODIMENTS First Embodiment

A high refractive index glass according to an embodiment of the firstinvention (hereinafter, referred to as first embodiment) comprises, as aglass composition in terms of mass %, 0 to 10% of B₂O₃, 0.001 to 35% ofSrO, 0.001 to 30% of ZrO₂+TiO₂, and 0 to 10% of La₂O₃+Nb₂O₅, and hasamass ratio of BaO/SrO of 0 to 40 and a mass ratio of SiO₂/SrO of 0.1 to40. The reasons why the content range of each component has beenrestricted as mentioned above are described below. Note that, in thefollowing description of the content range, the expression “%” refers to“mass %” unless otherwise specified.

The content of B₂O₃ is preferably 0 to 10%. As the content of B₂O₃increases in glass, its refractive index nd and Young's modulus areliable to lower. Thus, the upper limit range of B₂O₃ is suitably 8% orless, 5% or less, 4% or less, 3% or less, less than 2%, 1% or less,particularly suitably less than 1%.

The content of SrO is 0.001 to 35%. Among alkaline-earth metal oxides,SrO is a component that has a relatively large effect of increasing therefractive index nd of glass while suppressing its devitrificationproperty. However, when the content of SrO increases in glass, itsrefractive index nd, density, and thermal expansion coefficientincrease, and the balance among the components of the glass is lost inthe glass composition, with the result that its devitrificationresistance is liable to deteriorate. Thus, the upper limit range of SrOis suitably 30% or less, 25% or less, 20% or less, 15% or less, 12% orless, 10% or less, particularly suitably 8% or less. The lower limitrange of SrO is suitably 0.01% or more, 0.1% or more, 1% or more, 2% ormore, 3% or more, 3.5% or more, particularly suitably 4% or more.

The content of ZrO₂+TiO₂ is preferably 0.001 to 30%. When the content ofTiO₂+ZrO₂ increases in glass, its devitrification resistance may beliable to deteriorate and its density and thermal expansion coefficientmay be too high. On the other hand, when the content of TiO₂+ZrO₂decreases in glass, its refractive index nd is liable to lower. Thus,the upper limit range of TiO₂+ZrO₂ is suitably 25% or less, 20% or less,18% or less, 15% or less, 14% or less, particularly suitably 13% orless. The lower limit range of TiO₂+ZrO₂ is suitably 0.01% or more, 0.5%or more, 1% or more, 3% or more, 5% or more, 6% or more, particularlysuitably 7% or more.

The content of TiO₂ is preferably 0 to 30%. TiO₂ is a component thatincreases the refractive index nd of glass. However, when the content ofTiO₂ increases in glass, its density and thermal expansion coefficientare apt to become too high, its devitrification resistance is liable todeteriorate, and its transmittance tends to lower. Thus, the upper limitrange of TiO₂ is suitably 25% or less, 15% or less, 12% or less,particularly suitably 8% or less. The lower limit range of TiO₂ issuitably 0.001% or more, 0.01% or more, 0.5% or more, 1% or more,particularly suitably 3% or more.

The content of ZrO₂ is preferably 0 to 30%. ZrO₂ is a component that haslarge effects of increasing the refractive index nd of glass andincreasing the viscosity of glass at around its liquidus temperature.However, when the content of ZrO₂ increases in glass, its densitybecomes too high and its devitrification resistance is liable todeteriorate. Thus, the upper limit range of ZrO₂ is suitably 15% orless, 10% or less, 7% or less, particularly suitably 6% or less. Thelower limit range of ZrO₂ is suitably 0.001% or more, 0.01% or more,0.5% or more, 1% or more, 2% or more, particularly suitably 3% or more.

The content of La₂O₃+Nb₂O₅ is preferably 0 to 10%. When the content ofLa₂O₃+Nb₂O₅ increases in glass, its refractive index nd tends to behigher. However, when the content of La₂O₃+Nb₂O₅ is more than 10% inglass, the balance among the components of the glass is lost in theglass composition, resulting in the deterioration of its devitrificationresistance, and the material cost of the glass rises, possibly resultingin the surge of its production cost. Inexpensive glass is requiredparticularly in applications such as lighting devices, and hence anincrease in material cost is not preferred. Thus, the lower limit rangeof La₂O₃+Nb₂O₅ is suitably 8% or less, 5% or less, 3% or less, 2% orless, 1% or less, 0.5% or less, particularly suitably 0.1% or less.

La₂O₃ is a component that increases the refractive index nd of glass.When the content of La₂O₃ increases in glass, its devitrificationresistance is liable to deteriorate and its density and thermalexpansion coefficient may become too high. Thus, the content of La₂O₃ ispreferably 10% or less, 9% or less, 8% or less, 5% or less, 2% or less,1% or less, 0.5% or less, particularly preferably 0.1% or less.

Nb₂O₅ is a component that increases the refractive index nd of glass.When the content of Nb₂O₅ increases in glass, its devitrificationresistance is liable to deteriorate and its density and thermalexpansion coefficient may become too high. Thus, the content of Nb₂O₅ ispreferably 10% or less, 9% or less, 8% or less, 5% or less, 2% or less,1% or less, 0.5% or less, particularly preferably 0.1% or less.

The mass ratio of (La₂O₃+Nb₂O₅)/(ZrO₂+TiO₂) is preferably 0 to 30. Asthe mass ratio of (La₂O₃+Nb₂O₅)/(ZrO₂+TiO₂) is larger in glass, itsrefractive index nd can be increased while its devitrificationresistance is suppressed from deteriorating. However, when the value ofthe mass ratio is too large in glass, the balance among the componentsof the glass is lost in the glass composition, resulting in thedeterioration of its devitrification resistance, and the material costof the glass becomes too high. Thus, the upper limit range of the massratio of (La₂O₃+Nb₂O₅)/(ZrO₂+TiO₂) is suitably 20 or less, 10 or less, 5or less, 2 or less, 1 or less, 0.1 or less, particularly suitably 0.01or less.

The mass ratio of BaO/SrO is 0 to 40. When the mass ratio of BaO/SrO istoo large in glass, its devitrification resistance may deteriorate andits density and thermal expansion coefficient may become too high. Onthe other hand, when the mass ratio of BaO/SrO is too small in glass,its refractive index nd may lower, and the balance among the componentsof the glass is lost in the glass composition, possibly resulting in thedeterioration of its denitrification resistance. Thus, the upper limitrange of the mass ratio of BaO/SrO is suitably 30 or less, 20 or less,10 or less, 8 or less, particularly suitably 5 or less. The lower limitrange of the mass ratio of BaO/SrO is suitably 0.1 or more, 0.5 or more,1 or more, 2.5 or more, particularly suitably 3 or more.

Among alkaline-earth metal oxides, BaO is a component that increases therefractive index nd of glass without reducing its viscosity extremely.The content of BaO is preferably 0 to 40%. When the content of BaOincreases in glass, its refractive index nd, density, and thermalexpansion coefficient are apt to increase. However, when the content ofBaO is more than 40% in glass, the balance among the components of theglass is lost in the glass composition, with the result that itsdenitrification resistance is liable to deteriorate. Thus, the upperlimit range of BaO is suitably 35% or less, 32% or less, 30% or less,29.5% or less, 29% or less, particularly suitably 28% or less. Notethat, when the content of BaO decreases in glass, it becomes difficultfor the glass to have a desired refractive index nd and keep a highliquidus viscosity. Thus, the lower limit range of BaO is suitably 0.5%or more, 1% or more, 2% or more, 5% or more, 10% or more, 15% or more,17% or more, 20% or more, 23% or more, particularly suitably 25% ormore.

The mass ratio of SiO₂/SrO is 0.1 to 40. When the mass ratio of SiO₂/SrOis too large in glass, its refractive index nd is liable to lower. Onthe other hand, when the mass ratio of SiO₂/SrO is too small in glass,its denitrification resistance may deteriorate and its density andthermal expansion coefficient may become too high. Thus, the upper limitrange of the mass ratio of SiO₂/SrO is suitably 30 or less, 20 or less,15 or less, 10 or less, 9 or less, particularly suitably 8 or less. Thelower limit range of the mass ratio of SiO₂/SrO is suitably 0.5 or more,1 or more, 2 or more, 2.5 or more, particularly suitably 3 or more.

The content of SiO₂ is preferably 0.1 to 60%. When the content of SiO₂increases in glass, its meltability and formability are liable todeteriorate, and its refractive index nd is liable to lower. Thus, thecontent of SiO₂ is preferably 55% or less, 53% or less, 52% or less, 50%or less, 49% or less, 48% or less, particularly preferably 45% or less.On the other hand, when the content of SiO₂ decreases in glass, itsnetwork structure is not easily formed, resulting in difficulty invitrification, and the viscosity of the glass becomes too low, with theresult that it is difficult for the glass to keep a high liquidusviscosity. Thus, the content of SiO₂ is preferably 3% or more, 5% ormore, 10% or more, 15% or more, 20% or more, 25% or more, 30% or more,35% or more, particularly preferably 40% or more.

The content of Al₂O₃ is preferably 0 to 20%. When the content of Al₂O₃increases in glass, devitrified crystals are liable to deposit in theglass, its liquidus viscosity is liable to lower, and its refractiveindex nd is liable to lower. Thus, the upper limit range of Al₂O₃ issuitably 15% or less, 10% or less, 8% or less, particularly suitably 6%or less. Note that, when the content of Al₂O₃ decreases in glass, thebalance among the components of the glass is lost in the glasscomposition, with the result that the glass is also liable to denitrify.Thus, the lower limit range of Al₂O₃ is suitably 0.1% or more, 0.5% ormore, 1% or more, particularly suitably 3% or more.

The content of MgO is preferably 0 to 10%. MgO is a component thatincreases the refractive index nd of glass, its Young's modulus, and itsstrain point and is a component that decreases its viscosity at hightemperature. However, when MgO is added in a large amount in glass, itsliquidus temperature rises, with the result that its denitrificationresistance may deteriorate, and its density and thermal expansioncoefficient may become too high. Thus, the upper limit range of MgO issuitably 5% or less, 3% or less, 2% or less, 1.5% or less, 1% or less,particularly suitably 0.5% or less.

The content of CaO is preferably 0 to 10%. When the content of CaOincreases in glass, its density and thermal expansion coefficient areliable to be higher. Further, when the content of CaO is too large inglass, the balance among the components of the glass is lost in theglass composition, with the result that its devitrification resistanceis liable to deteriorate. Thus, the upper limit range of CaO is suitably9% or less, particularly suitably 8.5% or less. Note that, when thecontent of CaO decreases in glass, its meltability deteriorates, itsYoung's modulus lowers, and its refractive index nd is liable to lower.Thus, the lower limit range of CaO is suitably 0.5% or more, 1% or more,2% or more, 3% or more, particularly suitably 4% or more.

The mass ratio of (MgO+CaO)/SrO is preferably 0 to 20. When the massratio of (MgO+CaO)/SrO increases in glass, its density can be reducedand its viscosity at high temperature can be reduced while its highrefractive index nd is maintained, but its liquidus temperature isliable to increase, with the result that it is difficult to maintain itshigh liquidus viscosity. Thus, the upper limit range of the mass ratioof (MgO+CaO)/SrO is suitably 10 or less, 8 or less, 5 or less, 3 orless, 2 or less, particularly suitably 1 or less.

The content of ZnO is preferably 0 to 12%. When the content of ZnOincreases in glass, its density and thermal expansion coefficient becometoo high, the balance among the components of the glass is lost in theglass composition, with the result that its devitrification resistancedeteriorates, and its viscosity at high temperature lowers excessively,with the result that it is difficult to keep its high liquidusviscosity. Thus, the upper limit range of ZnO is suitably 8% or less, 4%or less, 2% or less, 1% or less, 0.5% or less, 0.1% or less,particularly suitably 0.01% or less.

The content of La₂O₃+Nb₂O₅+Gd₂O₃ is preferably 0 to 10%. When thecontent of La₂O₃+Nb₂O₅+Gd₂O₃ increases in glass, its refractive index ndtends to be higher. However, when the content of La₂O₃+Nb₂O₅+Gd₂O₃ ismore than 10% in glass, the balance among the components of the glass islost in the glass composition, resulting in the deterioration of itsdevitrification resistance, and the material cost of the glass rises,possibly resulting in the surge of its production cost. Inexpensiveglass is required particularly in applications such as lighting devices,and hence an increase in material cost is not preferred. Thus, the lowerlimit range of La₂O₃+Nb₂O₅+Gd₂O₃ is suitably 9% or less, 8% or less, 5%or less, 3% or less, 2% or less, 1% or less, 0.5% or less, particularlysuitably 0.1% or less.

The content of Gd₂O₃ is preferably 0 to 10%. Gd₂O₃ is a component thatincreases the refractive index of glass. However, when the content ofGd₂O₃ increases in glass, its density and thermal expansion coefficientbecome too high, the balance among the components of the glass is lostin the glass composition, with the result that its devitrificationresistance deteriorates, and its viscosity at high temperature lowersexcessively, with the result that it is difficult to keep its highliquidus viscosity. Thus, the upper limit range of Gd₂O₃ is suitably 8%or less, 4% or less, 2% or less, 1% or less, 0.5% or less, 0.1% or less,particularly suitably 0.01% or less.

The content of Li₂O+Na₂O+K₂O is preferably 0 to 15%. Li₂O+Na₂O+K₂O is acomponent that reduces the viscosity of glass and is a component thatadjusts its thermal expansion coefficient. However, when Li₂O+Na₂O+K₂Ois added in a large amount in glass, its viscosity lowers excessively,with the result that it is difficult to keep its high liquidusviscosity. Thus, the upper limit range of Li₂O+Na₂O+K₂O is suitably 10%or less, 5% or less, 2% or less, 1.5% or less, 1% or less, 0.5% or less,particularly suitably 0.1% or less.

As a fining agent, one kind or two or more kinds selected from the groupconsisting of As₂O₃, Sb₂O₃, CeO₂, SnO₂, F, Cl, and SO₃ may be added inan amount of 0 to 3%. Note that it is preferred to use As₂O₃, Sb₂O₃, andF, in particular, As₂O₃ and Sb₂O₃ in an amount as small as possible fromthe environmental viewpoint, and each of the contents thereof ispreferably less than 0.1%. In consideration of the above-mentionedpoints, SnO₂, SO₃, and Cl are each preferably used as the fining agent.In particular, the content of SnO₂ is preferably 0 to 1%, 0.01 to 0.5%,particularly preferably 0.05 to 0.4%. Further, the content ofSnO₂+SO₃+Cl is preferably 0 to 1%, 0.001 to 1%, 0.01 to 0.5%,particularly preferably 0.01 to 0.3%. Herein, the “SnO₂+SO₃+Cl” refersto the total amount of SnO₂, SO₃, and Cl.

PbO is a component that decreases the viscosity of glass at hightemperature, but is preferably used in an amount as small as possiblefrom the environmental viewpoint. The content of PbO is preferably 0.5%or less, more preferably less than 1,000 ppm (by mass).

Bi₂O₃ is a component that decreases the viscosity of glass at hightemperature, but is preferably used in an amount as small as possiblefrom the environmental viewpoint. The content of Bi₂O₃ is preferably0.5% or less, more preferably less than 1,000 ppm (by mass).

It is possible, as a matter of course, to construct suitable ranges ofthe composition of glass by combining each suitable content range ofeach component. Out of those suitable ranges, the particularly suitableranges of the composition of glass are the following ranges, from theviewpoints of the refractive index nd of glass, its denitrificationresistance, its production cost, and the like.

(1) A glass, comprising, as a glass composition in terms of mass %, 20to 50% of SiO₂, 0 to 8% of B₂O₃, 0 to 10% of CaO, 0.01 to 35% of SrO, 0to 30% of BaO, 0 to 4% of ZnO, 0.001 to 20% of ZrO₂+TiO₂, 0 to 3% ofLa₂O₃+Nb₂O₅, and 0 to 1% of Li₂O+Na₂O+K₂O, and having a mass ratio ofBaO/SrO of 0 to 20, a mass ratio of SiO₂/SrO of 1 to 15, and a massratio of (MgO+CaO)/SrO of 0 to 10.

(2) A glass, comprising, as a glass composition in terms of mass %, 35to 50% of SiO₂, 0 to 5% of B₂O₃, 0 to 9% of CaO, 1 to 35% of SrO, 0 to29% of BaO, 0 to 3% of ZnO, 1 to 15% of ZrO₂+TiO₂, 0 to 0.1% ofLa₂O₃+Nb₂O₅, and 0 to 0.1% of Li₂O+Na₂O+K₂O, and having a mass ratio ofBaO/SrO of 0 to 10, a mass ratio of SiO₂/SrO of 1 to 10, and a massratio of (MgO+CaO)/SrO of 0 to 5.

(3) A glass, comprising, as a glass composition in terms of mass %, 35to 50% of SiO₂, 0 to 3% of B₂O₃, 0 to 9% of CaO, 2 to 20% of SrO, 0 to28% of BaO, 0 to 1% of ZnO, 3 to 15% of ZrO₂+TiO₂, 0 to 0.1% ofLa₂O₃+Nb₂O₅, and 0 to 0.1% of Li₂O+Na₂O+K₂O, and having a mass ratio ofBaO/SrO of 0 to 8, a mass ratio of SiO₂/SrO of 2 to 10, and a mass ratioof (MgO+CaO)/SrO of 0 to 3.

(4) A glass, comprising, as a glass composition in terms of mass %, 35to 50% of SiO₂, 0 to 1% of B₂O₃, 0 to 8.5% of CaO, 4 to 15% of SrO, 0 to28% of BaO, 0 to 0.1% of ZnO, 6 to 15% of ZrO₂+TiO₂, 0 to 0.1% ofLa₂O₃+Nb₂O₅, and 0 to 0.1% of Li₂O+Na₂O+K₂O, and having a mass ratio ofBaO/SrO of 0 to 8, a mass ratio of SiO₂/SrO of 2 to 10, and a mass ratioof (MgO+CaO)/SrO of 0 to 3.

(5) A glass, comprising, as a glass composition in terms of mass %, 35to 55% of SiO₂, 0 to 8% of B₂O₃, 0.001 to 35% of SrO, 0 to 12% of ZnO,0.001 to 30% of ZrO₂+TiO₂, 0 to 5% of La₂O₃+Nb₂O₅, and 0 to 10% ofLi₂O+Na₂O+K₂O, and having a mass ratio of BaO/SrO of 0 to 20, a massratio of SiO₂/SrO of 0.1 to 20, and a mass ratio of (MgO+CaO)/SrO of 0to 20.

(6) A glass, comprising, as a glass composition in terms of mass %, 35to 55% of SiO₂, 0 to 5% of B₂O₃, 0 to 5% of MgO, 0 to 10% of ZrO₂, 0 to2% of Li₂O+Na₂O+K₂O, 0.1 to 20% of SrO, 0 to 30% of BaO, 0.001 to 15% ofTiO₂, and 0 to 9% of La₂O₃+Nb₂O₅+Gd₂O₃, and having a mass ratio of(La₂O₃+Nb₂O₅)/(ZrO₂+TiO₂) of 0 to 5, and a mass ratio of BaO/SrO of 0 to10.

(7) A glass, comprising, as a glass composition in terms of mass %, 35to 55% of SiO₂, 0 to 5% of B₂O₃, 0 to 5% of MgO, 0 to 10% of ZrO₂, 0 to2% of Li₂O+Na₂O+K₂O, 0.1 to 20% of SrO, 0 to 30% of BaO, 0.001 to 15% ofTiO₂, and 0 to 9% of La₂O₃+Nb₂O₅+Gd₂O₃, and having a mass ratio of(La₂O₃+Nb₂O₅)/(ZrO₂+TiO₂) of 0 to 5, a mass ratio of BaO/SrO of 0 to 10,a mass ratio of SiO₂/SrO of 0.1 to 10, and a mass ratio of (MgO+CaO)/SrOof 0 to 2.

The high refractive index glass of the first embodiment has a refractiveindex nd of 1.55 or more, more preferably 1.58 or more, 1.6 or more,1.63 or more, 1.65 or more, particularly preferably 1.66 or more. Whenthe refractive index nd is less than 1.55, the reflectance at theinterface between an ITO film and the glass becomes higher, and hencelight cannot be extracted efficiently. On the other hand, when therefractive index nd is more than 2.3, the reflectance at the interfacebetween air and the glass becomes higher, and hence it is difficult toenhance light extraction efficiency even if the surface of the glass issubjected to roughening treatment. Thus, the refractive index nd ispreferably 2.3 or less, 2.2 or less, 2.1 or less, 2.0 or less, 1.9 orless, particularly preferably 1.75 or less.

The high refractive index glass of the first embodiment has a liquidustemperature of preferably 1,200° C. or less, 1,150° C. or less, 1,130°C. or less, 1,110° C. or less, 1,090° C. or less, 1,070° C. or less,particularly preferably 1,050° C. or less. Further, the liquidusviscosity is preferably 10^(3.0) dPa·s or more, 10^(3.5) dPa·s or more,10^(3.8) dPa·s or more, 10^(4.0) dPa·s or more, 10^(4.1) dPa·s or more,10^(4.2) dPa·s or more, particularly preferably 10^(4.3) dPa·s or more.With this, it becomes difficult for the glass to denitrify at the timeof forming, and it becomes easier to form the glass into a glass sheetby a float method.

The high refractive index glass of the first embodiment preferably has asheet shape, and has a thickness of preferably 1.5 mm or less, 1.3 mm orless, 1.1 mm or less, 0.8 mm or less, 0.6 mm or less, 0.5 mm or less,0.3 mm or less, particularly preferably 0.2 mm or less. As the thicknessof the glass becomes smaller, its flexibility increases, and designdiversities of a lighting device can be easily increased. However, whenthe thickness of a glass sheet becomes extremely small, the glass sheetis liable to be damaged. Thus, the thickness of a glass sheet ispreferably 10 μm or more, particularly preferably 30 μm or more.

The high refractive index glass of the first embodiment is preferablyformed by a float method. With this, it is possible to produceunpolished glass sheets with good surface quality at low cost in largenumbers.

A method other than the float method, such as a down-draw method (e.g.,an overflow down-draw method, a slot down method, or a re-draw method)or a roll-out method, may also be adopted for forming glass into a glasssheet.

The high refractive index glass of the first embodiment is preferablysubjected to roughening treatment on one of its surfaces by HF etching,sandblasting, or the like. The surface roughness Ra of the rougheningtreated surface is preferably 10 Å or more, 20 Å or more, 30 Å or more,particularly preferably 50 Å or more. When the roughening treatedsurface is arranged on the side to be brought into contact with air ofan OLED lighting device or the like, because the roughening treatedsurface has a non-reflective structure, light produced in an organiclight-emitting layer does not easily return into the organiclight-emitting layer. As a result, light extraction efficiency can beenhanced. Further, irregularities may be provided in a surface of glassby thermal processing such as re-pressing. With this, a precisereflective structure can be formed in the surface of the glass. Theinterval and depth of the irregularities are recommended to be adjustedin consideration of the refractive index nd of the glass. Further, aresin film with irregularities may be attached on a surface of glass.

When atmospheric plasma processing is adopted, while the surfacecondition of one surface of a glass sheet is maintained, the othersurface of the glass sheet can be uniformly subjected to rougheningtreatment. Further, it is preferred to use a gas containing F (such asSF₆ or CF₄) as a source for the atmospheric plasma processing. Withthis, a plasma containing an HF-based gas is generated, and hence theefficiency of the roughening treatment is enhanced.

Note that, when a non-reflective structure is formed on a surface ofglass at the time of forming, the non-reflective structure can providethe same effect as that of roughening treatment even if the rougheningtreatment is not carried out.

The high refractive index glass of the first embodiment has a density ofpreferably 5.0 g/cm³ or less, 4.8 g/cm³ or less, 4.5 g/cm³ or less, 4.3g/cm³ or less, 3.7 g/cm³ or less, particularly preferably 3.5 g/cm³ orless. With this, the weight of the glass is reduced, and hence theweight of a device can be reduced. Note that the “density” can bemeasured by a well-known Archimedes method.

The high refractive index glass of the first embodiment has a thermalexpansion coefficient of preferably 30×10⁻⁷ to 100×10⁻⁷/° C., 40×10⁻⁷ to90×10⁻⁷/° C., 60×10⁻⁷ to 85×10⁻⁷/° C., 65×10⁻⁷ to 80×10⁻⁷/° C., 68×10⁻⁷to 78×10⁻⁷/° C., particularly preferably 70×10⁻⁷ to 78×10⁻⁷/° C. Inrecent years, the development of a glass sheet having flexibility hasbeen required in order to use the glass sheet in an OLED lightingdevice, an OLED device, and a dye-sensitized solar cell, from theviewpoint of improving their design elements. For enhancing theflexibility of a glass sheet, the thickness of the glass sheet needs tobe smaller. In this case, when the thermal expansion coefficient of theglass sheet does not match to that of a transparent conductive film suchas an ITO film or an FTO film, the glass sheet is liable to warp.Further, when an OLED display using an oxide TFT is manufactured, if thethermal expansion coefficient of the oxide TFT does not match to that ofa glass sheet, the glass sheet may have warpage or the film of the oxideTFT may have cracks. Thus, when the thermal expansion coefficient iscontrolled in any of the above-mentioned ranges, such a situation asdescribed above can be easily prevented. Herein, the “thermal expansioncoefficient” refers to an average value in the temperature range of 30to 380° C., and can be measured with, for example, a dilatometer.

The high refractive index glass of the first embodiment has a strainpoint of preferably 630° C. or more, 650° C. or more, 670° C. or more,690° C. or more, particularly preferably 700° C. or more. With this, theglass resists heat shrinkage even if high-temperature heat treatment isperformed during the production step of a device. Particularly when anOLED display is manufactured by using an oxide TFT or the like, heattreatment at about 600° C. is necessary for stabilizing the quality ofthe oxide TFT. When the strain point is restricted as described above,the heat shrinkage of the glass can be reduced in the heat treatment.

The high refractive index glass of the first embodiment has atemperature at 10^(2.5) dPa·s of preferably 1,400° C. or less, 1,350° C.or less, 1,300° C. or less, 1,250° C. or less, particularly preferably1,200° C. or less. With this, the meltability of the high refractiveindex glass improves. Hence, glass having excellent bubble quality canbe easily produced, and the production efficiency of a glass sheetimproves.

The high refractive index glass of the first embodiment has atemperature at 10^(4.0) dPa·s of preferably 1,250° C. or less, 1,200° C.or less, 1,150° C. or less, 1,110° C. or less, particularly preferably1,060° C. or less. With this, when the high refractive index glass isformed into a glass sheet by a float method, the forming temperaturethereof can be lowered. Consequently, a low-temperature operation can becarried out, a refractory used in a forming part has a longer servicelife, and the production cost of the glass sheet is easily reduced.

A method of producing the high refractive index glass of the firstembodiment is exemplified as follows. First, a glass batch ismanufactured by blending glass materials so that a desired glasscomposition is achieved. Next, the glass batch is melted and fined, andthe resultant molten glass is then formed into a desired shape.Subsequently, the resultant is subjected to annealing treatment asrequired and processed into a desired shape.

Note that a glass sheet for a lighting device according to an embodimentof the first invention comprises, as a glass composition in terms ofmass %, 0.1 to 60% of SiO₂, 0 to 10% of B₂O₃, 0.001 to 35% of SrO, 0 to40% of BaO, 0.001 to 30% of ZrO₂+TiO₂, and 0 to 10% of La₂O₃+Nb₂O₅, andhas a refractive index nd of 1.55 to 2.3. Further, a glass sheet for anOLED lighting device according to an embodiment of the first inventioncomprises, as a glass composition in terms of mass %, 0.1 to 60% ofSiO₂, 0 to 10% of B₂O₃, 0.001 to 35% of SrO, 0 to 40% of BaO, 0.001 to30% of ZrO₂+TiO₂, and 0 to 10% of La₂O₃+Nb₂O₅, and has a refractiveindex nd of 1.55 to 2.3. In addition, a glass sheet for an OLED displayaccording to an embodiment of the first invention comprises, as a glasscomposition in terms of mass %, 0.1 to 60% of SiO₂, 0 to 10% of B₂O₃,0.001 to 35% of SrO, 0 to 40% of BaO, 0.001 to 30% of ZrO₂+TiO₂, and 0to 10% of La₂O₃+Nb₂O₅, and has a refractive index nd of 1.55 to 2.3. Theglass sheet for a lighting device, the glass sheet for an OLED lightingdevice, and the glass sheet for an OLED display each have substantiallythe same technical features as those of the high refractive index glassdescribed in the first embodiment above, and hence the detaileddescription thereof is omitted here for convenience sake.

Example 1

Hereinafter, examples of the first invention are described in detail.Note that the following examples are merely for illustrative purposes.The first invention is by no means limited to the following examples.

Tables 1 to 4 show examples of the first invention (Sample Nos. 1 to19).

TABLE 1 Example No. 1 No. 2 No. 3 No. 4 No. 5 Glass SiO₂ 42.0 42.0 45.045.0 45.0 composition Al₂O₃ 5.0 5.0 5.0 5.0 5.0 [mass %] B₂O₃ — 3.0 — —6.0 CaO 5.9 5.9 5.9 5.9 5.9 SrO 7.9 4.9 7.9 10.9 4.9 BaO 26.2 26.2 26.226.2 26.2 ZrO₂ 3.0 3.0 3.0 3.0 3.0 TiO₂ 10.0 10.0 7.0 4.0 4.0 ZrO₂ +TiO₂ 13.0 13.0 10.0 7.0 7.0 La₂O₃ + Nb₂O₅ 0 0 0 0 0 SiO₂/SrO 5.3 8.6 5.74.1 9.2 BaO/SrO 3.3 5.3 3.3 2.4 5.3 (MgO + CaO)/SrO 0.7 1.2 0.7 0.5 1.2Density [g/cm³] 3.39 3.29 3.33 3.36 3.27 Thermal expansion 72 69 71 7468 coefficient [×10⁻⁷/° C.] 30 to 380° C. Ps [° C.] 700 667 698 692 646Ta [° C.] 741 706 740 736 686 Ts [° C.] 885 852 894 895 840 10⁴ dPa · s[° C.┘] 1,068 1,040 1,099 1,105 1,052 10³ dPa · s [° C.] 1,165 1,1371,203 1,212 1,162 10^(2.5) dPa · s [° C.] 1,229 1,204 1,273 1,284 1,236TL [° C.] 1,110 1,075 1,088 1,083 1,087 log₁₀ηTL [dPa · s] 3.5 3.6 4.14.3 3.6 Refractive index nd 1.67 1.66 1.64 1.63 1.61 λ = 587.6 nm

TABLE 2 Example No. 6 No. 7 No. 8 No. 9 Glass SiO₂ 42.0 45.0 39.0 42.0composition Al₂O₃ 5.0 5.0 5.0 5.0 [mass %] B₂O₃ — — 4.0 — CaO 5.9 5.96.0 6.0 SrO 7.9 4.9 10.0 10.0 BaO 26.2 29.2 28.0 28.0 ZrO₂ 6.0 3.0 5.05.0 TiO₂ 7.0 7.0 3.0 4.0 ZrO₂ + TiO₂ 13.0 10.0 8.0 9.0 La₂O₃ + Nb₂O₅ 0 00 0 SiO₂/SrO 5.3 9.2 3.9 4.2 BaO/SrO 3.3 6.0 2.8 2.8 (MgO + CaO)/SrO 0.71.2 0.6 0.6 Density [g/cm³] 3.41 3.32 3.44 3.45 Thermal expansion 72 7076 76 coefficient [×10⁻⁷/° C.] 30 to 380° C. Ps [° C.] 712 696 658 705Ta [° C.] 755 738 698 748 Ts [° C.] 907 895 848 904 10⁴ dPa · s [° C.]1,104 1,101 1,040 1,104 10³ dPa · s [° C.] 1,202 1,208 1,134 1,20310^(2.5) dPa · s [° C.] 1,268 1,280 1,196 1,268 TL [° C.] 1,090 1,1001,045 1,100 log₁₀ηTL [dPa · s] 4.2 4.0 3.9 4.1 Refractive index nd 1.661.64 1.64 1.64 λ = 587.6 nm

TABLE 3 Example No. 10 No. 11 No. 12 No. 13 No. 14 Glass SiO₂ 50.0 40.047.5 42.5 45.0 composition Al₂O₃ — 10.0 2.5 7.5 5.0 [mass %] CaO 5.9 5.95.9 5.9 7.9 SrO 10.9 10.9 10.9 10.9 10.9 BaO 26.2 26.2 26.2 26.2 24.2ZrO₂ 3.0 3.0 3.0 3.0 3.0 TiO₂ 4.0 4.0 4.0 4.0 4.0 ZrO₂ + TiO₂ 7.0 7.07.0 7.0 7.0 La₂O₃ + Nb₂O₅ 1.0 2.0 3.0 4.0 0 SiO₂/SrO 4.6 3.7 4.4 3.9 4.1BaO/SrO 2.4 2.4 2.4 2.4 2.2 (MgO + CaO)/SrO 0.5 0.5 0.5 0.5 0.7 Density[g/cm³] 3.33 3.39 3.37 3.38 3.35 Thermal expansion 75 73 74 74 76coefficient [×10⁻⁷/° C.] 30 to 380° C. Ps [° C.] 682 710 702 669 691 Ta[° C.] 724 754 746 711 735 Ts [° C.] 881 913 904 865 892 10⁴ dPa · s [°C.] 1,098 1,119 1,112 1,066 1,096 10³ dPa · s [° C.] 1,204 1,223 1,2181,166 1,199 10^(2.5) dPa · s [° C.] 1,276 1,292 1,288 1,232 1,269 TL [°C.] Not Not 1,169 1,083 Not evaluated evaluated evaluated log₁₀ηTL [dPa· s] Not Not 3.4 3.8 Not evaluated evaluated evaluated Refractive indexnd 1.62 1.63 1.63 1.64 1.63 λ = 587.6 nm

TABLE 4 Example No. 15 No. 16 No. 17 No. 18 No. 19 Glass SiO₂ 45.0 45.045.0 45.0 45.0 composition Al₂O₃ 5.0 5.0 5.0 5.0 5.0 [mass %] CaO 3.93.9 7.9 5.9 5.9 SrO 10.9 10.9 10.9 10.9 10.9 BaO 28.2 26.2 26.2 24.228.2 ZrO₂ 3.0 5.0 1.0 5.0 1.0 TiO₂ 4.0 4.0 4.0 4.0 4.0 ZrO₂ + TiO₂ 7.09.0 5.0 9.0 5.0 La₂O₃ + Nb₂O₅ 0 0 0 0 0 SiO₂/SrO 4.1 4.1 4.1 4.1 4.1BaO/SrO 2.6 2.4 2.4 2.2 2.6 (MgO + CaO)/SrO 0.4 0.4 0.7 0.5 0.5 Density[g/cm³] 3.37 3.36 3.36 3.35 3.37 Thermal expansion 72 70 78 71 77coefficient [×10⁻⁷/° C.] 30 to 380° C. Ps [° C.] 693 701 683 700 684 Ta[° C.] 737 746 726 745 727 Ts [° C.] 898 909 881 906 884 10⁴ dPa · s [°C.] 1,114 1,126 1,084 1,117 1,093 10³ dPa · s [° C.] 1,225 1,238 1,1861,225 1,199 10^(2.5) dPa · s [° C.] 1,299 1,313 1,255 1,298 1,270 TL [°C.] Not Not Not Not Not evaluated evaluated evaluated evaluatedevaluated log₁₀ηTL [dPa · s] Not Not Not Not Not evaluated evaluatedevaluated evaluated evaluated Refractive index nd 1.63 1.63 1.63 1.641.63 λ = 587.6 nm

First, glass materials were blended so that each glass compositiondescribed in Tables 1 to 4 was achieved. After that, the resultant glassbatch was fed into a glass melting furnace and melted at 1,500 to 1,600°C. for 4 hours. Next, the resultant molten glass was poured on a carbonsheet to be formed into a glass sheet, followed by predeterminedannealing treatment. Finally, the resultant glass sheet was evaluatedfor its various characteristics.

The density is a value obtained by measurement using a well-knownArchimedes method.

The thermal expansion coefficient is a value obtained by measurement ofan average thermal expansion coefficient at 30 to 380° C. with adilatometer. A cylindrical sample (having end surfaces subjected to Rprocessing) having a size of 5 mm in diameter by 20 mm in length wasused as a measurement sample.

The strain point Ps is a value obtained by measurement based on a methodas described in ASTM C336-71. Note that, as the strain point Ps becomeshigher, the heat resistance becomes higher.

The annealing point Ta and the softening point Ts are values obtained bymeasurement based on a method as described in ASTM C338-93.

The temperatures at viscosities of 10^(4.0) dPa·s, 10^(3.0) dPa·s, and10^(2.5) dPa·s are values obtained by measurement using a platinumsphere pull up method. Note that, as each of the temperatures becomeslower, the meltability becomes more excellent.

The liquidus temperature TL is a value obtained by measuring atemperature at which crystals of glass deposit when glass powder thathas passed through a standard 30-mesh sieve (500 μm) and remained on a50-mesh sieve (300 μm) is placed in a platinum boat and kept in agradient heating furnace for 24 hours. Further, the liquidus viscositylog₁₀ηTL is a value obtained by measuring the viscosity of glass at itsliquidus temperature by a platinum sphere pull up method. Note that, asthe liquidus viscosity becomes higher and the liquidus temperaturebecomes lower, each of the denitrification resistance and theformability becomes more excellent.

The refractive index nd is a value obtained by producing samples havinga rectangular parallelepiped shape of 25 mm by 25 mm by about 3 mm, thensubjecting the samples to annealing treatment at a cooling rate of 0.1°C./min in the temperature range from (annealing point Ta+30° C.) to(strain point Ps-50° C.), and subsequently measuring the refractiveindex nd with a refractometer KPR-2000 manufactured by ShimadzuCorporation in a state in which an immersion liquid having a refractiveindex nd matching to that of the samples is immersed between two glasssamples.

Example 2

Glass materials were blended so that the glass composition described inSample No. 3 was achieved, and then the resultant glass batch was loadedinto a continuous kiln and melted at a temperature of 1,500 to 1,600° C.Subsequently, the resultant molten glass was formed into a glass sheethaving a thickness of 0.5 mm by a float method.

Glass materials were blended so that the glass composition described inSample No. 4 was achieved, and then the resultant glass batch was loadedinto a continuous kiln and melted at a temperature of 1,500 to 1,600° C.Subsequently, the resultant molten glass was formed into a glass sheethaving a thickness of 0.5 mm by a float method.

Glass materials were blended so that the glass composition described inSample No. 6 was achieved, and then the resultant glass batch was loadedinto a continuous kiln and melted at a temperature of 1,500 to 1,600° C.Subsequently, the resultant molten glass was formed into a glass sheethaving a thickness of 0.5 mm by a float method.

Second Embodiment

A high refractive index glass according to an embodiment of the secondinvention (hereinafter, referred to as second embodiment) comprises, asa glass composition in terms of mass %, 30 to 60% of SiO₂, 0 to 15% ofB₂O₃, 0 to 15% of Al₂O₃, 0 to 10% of Li₂O, 0 to 10% of Na₂O, 0 to 10% ofK₂O, 20 to 60% of MgO+CaO+SrO+BaO+ZnO, 0.0001 to 20% of TiO₂, 0 to 20%of ZrO₂, and 0 to 10% of La₂O₃+Nb₂O₅. The reasons why the content rangeof each component has been restricted as mentioned above are describedbelow. Note that, in the description of the content range of eachcomponent, “%” refers to “mass %” unless otherwise specified.

The content of SiO₂ is 30 to 60%. When the content of SiO₂ increases inglass, its meltability and formability are liable to deteriorate, andits refractive index nd is liable to lower. Thus, the upper limit of thecontent of SiO₂ is 60% or less, preferably 50% or less, 48% or less, 45%or less, particularly preferably 43% or less. On the other hand, whenthe content of SiO₂ decreases in glass, its network structure is noteasily formed, resulting in difficulty in vitrification, the viscosityof the glass becomes too low, with the result that it is difficult forthe glass to keep a high liquidus viscosity, and its acid resistance isliable to lower. Thus, the lower limit of the content of SiO₂ is 30% ormore, preferably 35% or more, 38% or more, particularly preferably 40%or more.

The content of B₂O₃ is 0 to 15%. When the content of B₂O₃ increases inglass, its Young's modulus is liable to lower and its strain point isliable to lower. Moreover, the balance among the components of the glassis impaired in the glass composition, with the result that itsdenitrification resistance is liable to deteriorate and its acidresistance is liable to deteriorate. Thus, the upper limit of thecontent of B₂O₃ is 15% or less, preferably 10% or less, 8% or less,particularly preferably 6% or less. On the other hand, if the content ofthe B₂O₃ is small, the liquidus viscosity of the glass easily lowers.Thus, the lower limit content of B₂O₃ is suitably 0.1% or more, 0.5% ormore, 1% or more, 1.5% or more, 2% or more, 3% or more, particularlysuitably 4% or more.

The mass ratio of B₂O₃/SiO₂ is preferably 0 to 1. When the mass ratio ofB₂O₃/SiO₂ increases in glass, it becomes difficult for the glass to keepa high liquidus viscosity and its chemical resistance is liable todeteriorate. Thus, the upper limit range of the mass ratio of B₂O₃/SiO₂is suitably 1 or less, 0.5 or less, 0.2 or less, 0.15 or less,particularly suitably 0.13 or less. On the other hand, when the massratio of B₂O₃/SiO₂ decreases in glass, the balance among the componentsof the glass is impaired in the glass composition, with the result thatits devitrification resistance is liable to deteriorate. Thus, the lowerlimit range of the mass ratio of B₂O₃/SiO₂ is suitably 0.01 or more,0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, particularlysuitably 0.10 or more.

The content of Al₂O₃ is 0 to 15%. When the content of Al₂O₃ is too largein glass, the balance among the components of the glass is impaired inthe glass composition, with the results that its devitrificationresistance is liable to deteriorate and its acid resistance is liable todeteriorate. Thus, the upper limit of the content of Al₂O₃ is 15% orless, preferably 10% or less, 8% or less, particularly preferably 6% orless. On the other hand, when the content of Al₂O₃ decreases in glass,its viscosity becomes too low, with the result that it is difficult forthe glass to keep a high liquidus viscosity. Thus, the lower limitcontent of Al₂O₃ is suitably 0.5% or more, 1% or more, 2% or more,particularly suitably 4% or more.

The content of Li₂O is 0 to 10%. When the content of Li₂O increases inglass, its liquidus viscosity is liable to lower, its strain point isliable to lower, and the elution of the alkali component in an etchingstep with acid easily causes the glass to be cloudy. Thus, the upperlimit of the content of Li₂O is 10% or less, preferably 8% or less, 5%or less, 4% or less, 3% or less, less than 2%, 1% or less, particularlypreferably less than 1%, and it is desirable that glass be substantiallyfree of Li₂O. Herein, the phrase “substantially free of Li₂O” refers tothe case where the content of Li₂O in a glass composition is less than1,000 ppm (by mass).

The content of Na₂O is 0 to 10%. When the content of Na₂O increases inglass, its liquidus viscosity is liable to lower, its strain point isliable to lower, and the elution of the alkali component in an etchingstep with acid easily causes the glass to be cloudy. Thus, the upperlimit of the content of Na₂O is 10% or less, preferably 8% or less, 5%or less, 4% or less, 3% or less, less than 2%, 1% or less, particularlypreferably less than 1%, and it is desirable that glass be substantiallyfree of Na₂O. Herein, the phrase “substantially free of Na₂O” refers tothe case where the content of Na₂O in a glass composition is less than1,000 ppm (by mass).

The content of K₂O is 0 to 10%. When the content of K₂O increases inglass, its liquidus viscosity is liable to lower, its strain point isliable to lower, and the elution of the alkali component in an etchingstep with acid easily causes the glass to be cloudy. Thus, the upperlimit of the content of K₂O is 10% or less, preferably 8% or less, 5% orless, 4% or less, 3% or less, less than 2%, 1% or less, particularlypreferably less than 1%, and it is desirable that glass be substantiallyfree of K₂O. Herein, the phrase “substantially free of K₂O” refers tothe case where the content of K₂O in a glass composition is less than1,000 ppm (by mass).

The content of Li₂O+Na₂O+K₂O is 0 to 10%. When the content ofLi₂O+Na₂O+K₂O increases in glass, its liquidus viscosity is liable tolower, its strain point is liable to lower, and the elution of thealkali component in an etching step with acid easily causes the glass tobe cloudy. Thus, the upper limit of the content of Li₂O+Na₂O+K₂O is 10%or less, 8% or less, 5% or less, 4% or less, 3% or less, 2% or less, 1%or less, particularly less than 1%, and it is desirable that glass besubstantially free of Li₂O+Na₂O+K₂O. Herein, the phrase “substantiallyfree of Li₂O+Na₂O+K₂O” refers to the case where the content ofLi₂O+Na₂O+K₂O in a glass composition is less than 1,000 ppm (by mass).

The content of MgO is preferably 0 to 20%. MgO is a component thatincreases the refractive index nd of glass, its Young's modulus, and itsstrain point and is a component that decreases its viscosity at hightemperature. However, when MgO is contained in a large amount in glass,its liquidus temperature rises, with the result that its denitrificationresistance may deteriorate and its density and thermal expansioncoefficient may become too high. Thus, the upper limit content of MgO issuitably 20% or less, 10% or less, particularly suitably 6% or less. Onthe other hand, when the content of MgO decreases in glass, itsmeltability deteriorates, its Young's modulus lowers, and its refractiveindex nd is liable to lower. Thus, the lower limit content of MgO issuitably 0.1% or more, 0.5% or more, 1% or more, 1.5% or more, 2% ormore, particularly suitably 3% or more.

The content of CaO is preferably 0 to 15%. When the content of CaOincreases in glass, its density and thermal expansion coefficient areliable to be higher, and the balance among the components of the glassis impaired in the glass composition, with the result that itsdevitrification resistance is liable to deteriorate. Thus, the upperlimit content of CaO is suitably 15% or less, 13% or less, 11% or less,9.5% or less, particularly suitably 8% or less. On the other hand, whenthe content of CaO decreases in glass, its meltability deteriorates, itsYoung's modulus lowers, and its refractive index nd is liable to lower.Thus, the lower limit content of CaO is suitably 0.5% or more, 1% ormore, particularly suitably 2% or more.

The content of SrO is preferably 0 to 25%. When the content of SrOincreases in glass, its refractive index nd, density, and thermalexpansion coefficient are liable to be higher, and the balance among thecomponents of the glass is impaired in the glass composition, with theresult that its devitrification resistance is liable to deteriorate.Thus, the upper limit content of SrO is suitably 25% or less, 18% orless, 14% or less, particularly suitably 12% or less. On the other hand,when the content of SrO decreases in glass, its meltability is liable todeteriorate and its refractive index nd is liable to lower. Thus, thelower limit content of SrO is suitably 0.1% or more, 0.5% or more, 1% ormore, 2% or more, 5% or more, 7% or more, particularly suitably 9% ormore.

Among alkaline-earth metal oxides, BaO is a component that increases therefractive index nd of glass without reducing its viscosity extremely,and the content of BaO is preferably 0.1 to 60%. When the content of BaOincreases in glass, its refractive index nd, density, and thermalexpansion coefficient are apt to increase, and the balance among thecomponents of the glass is impaired in the glass composition, with theresult that its devitrification resistance is liable to deteriorate.Thus, the upper limit content of BaO is suitably 60% or less, 53% orless, 48% or less, 44% or less, 40% or less, 39% or less, 36% or less,35% or less, 34% or less, particularly suitably 33% or less. On theother hand, when the content of BaO decreases in glass, it becomesdifficult for the glass to have a desired refractive index nd and keep ahigh liquidus viscosity. Thus, the upper limit content of BaO issuitably 0.1% or more, 1% or more, 2% or more, 5% or more, 10% or more,15% or more, 20% or more, 23% or more, particularly suitably 25% ormore.

The content of ZnO is preferably 0 to 20%. ZnO is a component thatincreases the refractive index nd of glass and its strain point and is acomponent that decreases its viscosity at high temperature. However,when ZnO is added in a large amount in glass, its liquidus temperaturerises, with the result that its devitrification resistance maydeteriorate and its density and thermal expansion coefficient may becometoo high. Thus, the upper limit content of ZnO is suitably 20% or less,10% or less, 5% or less, 3% or less, particularly suitably 1% or less.

The content of MgO+CaO+SrO+BaO+ZnO is 20 to 60%. When the content ofMgO+CaO+SrO+BaO+ZnO increases in glass, its density and thermalexpansion coefficient tend to increase, and the balance among thecomponents of the glass is impaired in the glass composition, with theresult that its devitrification resistance is liable to deteriorate.Thus, the upper limit content of MgO+CaO+SrO+BaO+ZnO is 60% or less,preferably 55% or less, 50% or less, 48% or less, particularlypreferably 45% or less. On the other hand, when the content ofMgO+CaO+SrO+BaO+ZnO decreases in glass, the glass becomes unstableresults. Thus, the lower limit of the content of MgO+CaO+SrO+BaO+ZnO is20% or more, preferably 30% or more, 35% or more, particularlypreferably 40% or more.

TiO₂ is a component that increases the refractive index nd of glass. Thecontent of TiO₂ is 0.0001 to 20%. However, when the content of TiO₂increases in glass, the balance among the components of the glass isimpaired in the glass composition, with the result that itsdevitrification resistance is liable to deteriorate. In addition, thetransmittance of the glass reduces, and when the glass is applied in anOLED display, its light-emitting efficiency may deteriorate. Thus, theupper limit of the content of TiO₂ is 20% or less, preferably 10% orless, 7% or less, particularly preferably 5% or less. On the other hand,when the content of TiO₂ decreases in glass, a desired refractive indexnd is not easily provided to the glass. Thus, the lower limit of thecontent of TiO₂ is 0.0001% or more, preferably 0.001% or more, 0.01% ormore, 0.02% or more, 0.05% or more, 0.1% or more, 1% or more,particularly preferably 2% or more.

ZrO₂ is a component that increases the refractive index nd of glass. Thecontent of ZrO₂ is 0 to 20%. However, when the content of ZrO₂ increasesin glass, the balance among the components of the glass is impaired inthe glass composition, with the result that its devitrificationresistance is liable to deteriorate. Thus, the upper limit of thecontent of ZrO₂ is 20% or less, preferably 10% or less, 7% or less,particularly preferably 5% or less. On the other hand, when the contentof ZrO₂ decreases in glass, a desired refractive index nd is not easilyprovided to the glass. Thus, the lower limit content of ZrO₂ is 0.0001%or more, preferably 0.001% or more, 0.01% or more, 0.02% or more, 0.05%or more, 0.1% or more, 1% or more, particularly preferably 2% or more.

La₂O₃ is a component that increases the refractive index nd of glass.The content of La₂O₃ is preferably 0 to 10%. When the content of La₂O₃increases in glass, its density and thermal expansion coefficient tendto increase and its devitrification resistance and acid resistance areliable to deteriorate. In addition, the material cost of the glassrises, with the result that the production cost of a glass sheet madefrom the glass is liable to surge. Thus, the upper limit content ofLa₂O₃ is suitably 10% or less, 5% or less, 3% or less, 2.5% or less,particularly suitably 1% or less.

Nb₂O₅ is a component that increases the refractive index nd of glass.The content of Nb₂O₅ is preferably 0 to 10%. When the content of Nb₂O₅increases in glass, its density and thermal expansion coefficient tendto increase and its devitrification resistance is liable to deteriorate.In addition, the material cost of the glass rises, with the result thatthe production cost of a glass sheet made from the glass is liable tosurge. Thus, the upper limit content of Nb₂O₅ is suitably 10% or less,5% or less, 3% or less, particularly suitably 1% or less.

The content of Gd₂O₃ is preferably 0 to 10%. Gd₂O₃ is a component thatincreases the refractive index nd of glass. However, when the content ofGd₂O₃ increases in glass, its density and thermal expansion coefficientbecome too high, the balance among the components of the glass is lostin the glass composition, with the result that its devitrificationresistance deteriorates, and its viscosity at high temperature lowersexcessively, with the result that it is difficult for the glass to keepa high liquidus viscosity. Thus, the upper limit content of Gd₂O₃ issuitably 10% or less, 5% or less, 3% or less, particularly suitably 1%or less.

The content of La₂O₃+Nb₂O₅ is 0 to 10%. When the content of La₂O₃+Nb₂O₅increases in glass, its density and thermal expansion coefficient tendto increase, its devitrification resistance is liable to deteriorate,and it is difficult for the glass to keep a high liquidus viscosity. Inaddition, the material cost of the glass rises, with the result that theproduction cost of a glass sheet made from the glass is liable to surge.Thus, the upper limit of the content of La₂O₃+Nb₂O₅ is 10% or less,preferably 8% or less, 5% or less, 3% or less, 1% or less, 0.5% or less,particularly preferably 0.1% or less.

The total content of rare metal oxides is preferably 0 to 10%. When thetotal content of rare metal oxides increases in glass, its density andthermal expansion coefficient tend to be higher, its denitrificationresistance and acid resistance are liable to deteriorate, and it becomesdifficult for the glass to keep a high liquidus viscosity. In addition,the material cost of the glass rises, with the result that theproduction cost of a glass sheet made from the glass tends to surge.Thus, the upper limit content of rare metal oxides is suitably 10% orless, 5% or less, 3% or less, particularly suitably 1% or less.

The following components may be added in addition to the above-mentionedcomponents.

As a fining agent, one kind or two or more kinds selected from the groupconsisting of As₂O₃, Sb₂O₃, CeO₂, SnO₂, F, Cl, and SO₃ may be added inan amount of 0 to 3%. Note that it is preferred to use As₂O₃, Sb₂O₃, andF in an amount as small as possible from the environmental viewpoint,and each of the contents thereof is preferably less than 0.1%. Inconsideration of the above-mentioned points, SnO₂, SO₃, Cl, and CeO₂ areeach preferably used as the fining agent.

The content of SnO₂ is preferably 0 to 1%, 0.001 to 1%, particularlypreferably 0.01 to 0.5%.

The content of SO₃ is preferably 0 to 1%, 0 to 0.5%, 0.001 to 0.1%,0.005 to 0.1%, 0.01 to 0.1%, particularly preferably 0.01 to 0.05%.Sodium sulfate may be used as a material for introducing SO₃. Further, amaterial containing sulfuric acid may also be used.

The content of Cl is preferably 0 to 1%, 0.001 to 0.5%, particularlypreferably 0.01 to 0.4%.

The content of SnO₂+SO₃+Cl is preferably 0 to 1%, 0.001 to 1%, 0.01 to0.5%, particularly preferably 0.01 to 0.3%. Herein, the “SnO₂+SO₃+Cl”refers to the total amount of SnO₂, SO₃, and Cl.

The content of CeO₂ is preferably 0 to 6%. When the content of CeO₂increases in glass, its denitrification resistance is liable to lower.Thus, the upper limit content of CeO₂ is suitably 6% or less, 5% orless, 3% or less, 2% or less, particularly suitably 1% or less. On theother hand, when the content of CeO₂ decreases in glass, the effect as afining agent is lessened. Thus, the lower limit content of CeO₂ issuitably 0.001% or more, 0.005% or more, 0.01% or more, 0.05% or more,particularly suitably 0.1% or more.

PbO is a component that decreases the viscosity of glass at hightemperature, but is preferably used in an amount as small as possiblefrom the environmental viewpoint. The content of PbO is preferably 0.5%or less, and it is desirable that glass be substantially free of PbO.Herein, the phrase “substantially free of PbO” refers to the case wherethe content of PbO in a glass composition is less than 1,000 ppm (bymass).

It is possible to construct suitable ranges of the composition of glassby combining the suitable range of each component. Of those, suitableranges of the composition of glass are as follows.

(1) A glass comprising, in terms of mass %, 30 to 60% of SiO₂, 0 to 15%of B₂O₃, 0 to 15% of Al₂O₃, 0 to 10% of Li₂O, 0 to 10% of Na₂O, 0 to 10%of K₂O %, 20 to 60% of MgO+CaO+SrO+BaO+ZnO, 0.1 to 20% of TiO₂, 0 to 20%of ZrO₂, and 0 to 10% of La₂O₃+Nb₂O₅.

(2) A glass comprising, in terms of mass %, 35 to 45% of SiO₂, 2 to 8%of B₂O₃, 4 to 8% of Al₂O₃, 1 to 8% of Li₂O, 0 to 5% of Na₂O, 0 to 8% ofK₂O, 30 to 48% of MgO+CaO+SrO+BaO+ZnO, 1 to 7% of TiO₂, 0.1 to 5% ofZrO₂, and 0 to 5% of La₂O₃+Nb₂O₅.

The high refractive index glass of the second embodiment has arefractive index nd of 1.55 or more, preferably 1.58 or more, 1.60 ormore, particularly preferably 1.63 or more. When the refractive index ndis less than 1.55, light cannot be extracted efficiently owing to thereflectance at the interface between a transparent conductive film and aglass sheet. On the other hand, when the refractive index nd is morethan 2.3, the reflectance at the interface between air and a glass sheetbecomes higher, and hence it is difficult to extract light to theoutside even if the surface of the glass is subjected to rougheningtreatment. Thus, the refractive index nd is 2.3 or less, preferably 2.2or less, 2.1 or less, 2.0 or less, 1.9 or less, particularly preferably1.75 or less.

The high refractive index glass of the second embodiment has a densityof preferably 5.0 g/cm³ or less, 4.8 g/cm³ or less, 4.5 g/cm³ or less,4.3 g/cm³ or less, 3.7 g/cm³ or less, 3.5 g/cm³ or less, particularlypreferably 3.4 g/cm³ or less. With this, the weight of a device can bereduced.

The high refractive index glass of the second embodiment has a thermalexpansion coefficient at 30 to 380° C. of preferably 45×10⁻⁷ to110×10⁻⁷/° C., 50×10⁻⁷ to 100×10⁻⁷/° C., 60×10⁻⁷ to 95×10⁻⁷/° C.,65×10⁻⁷ to 90×10⁻⁷/° C., 65×10⁻⁷ to 85×10⁻⁷/° C., particularlypreferably 67×10⁻⁷ to 80×10⁻⁷/° C. In recent years, flexibility has beenimparted to a glass sheet in some cases from the viewpoint of improvingdesign elements in an OLED device and the like. For enhancing theflexibility of a glass sheet, the thickness of the glass sheet needs tobe smaller. In this case, when the thermal expansion coefficient of theglass sheet does not match to that of a transparent conductive film, theglass sheet is liable to warp. Thus, when the thermal expansioncoefficient at 30 to 380° C. is controlled in any of the above-mentionedranges, such a situation as described above can be easily prevented.

The high refractive index glass of the second embodiment has a strainpoint of preferably 600° C. or more, particularly preferably 630° C. ormore. When a transparent conductive film is formed for a device such asan organic thin-film solar cell, as treatment is performed at a highertemperature, the formed film has higher transparency and lower electricresistance. However, conventional high refractive index glass hadinsufficient heat resistance, and hence it was difficult to strike abalance between high transparency and low electric resistance. Thus,when the strain point of the high refractive index glass is controlledin the above-mentioned range, it is possible to strike a balance betweenhigh transparency and low electric resistance in a device such as anorganic thin-film solar cell in which the glass is used, and the glassresists thermal shrinkage even if thermal treatment is carried out inthe production process of the device.

The high refractive index glass of the second embodiment has atemperature at 10^(2.5) dPa·s of preferably 1,450° C. or less, 1,400° C.or less, 1,350° C. or less, 1,300° C. or less, 1,250° C. or less,particularly preferably 1,200° C. or less. With this, the meltability ofthe high refractive index glass improves. Hence, the productionefficiency of the glass improves.

The high refractive index glass of the second embodiment invention has aliquidus temperature of preferably 1,200° C. or less, 1,150° C. or less,1,130° C. or less, 1,110° C. or less, 1,090° C. or less, 1,070° C. orless, 1,050° C. or less, 1,040° C. or less, 1,000° C. or less,particularly preferably 980° C. or less. Further, the liquidus viscosityis preferably 10^(3.5) dPa·s or more, 10^(3.8) dPa·s or more, 10^(4.0)dPa·s or more, 10^(4.2) dPa·s or more, 10^(4.4) dPa·s or more, 10^(4.6)dPa·s or more, 10^(4.8) dPa·s or more, particularly preferably 10^(5.0)dPa·s or more. With this, it becomes difficult for the glass todenitrify at the time of forming, and it becomes easier to form theglass into a glass sheet by a float method or an overflow down-drawmethod.

The high refractive index glass of the second embodiment preferably hasa sheet shape, and has a thickness (sheet thickness in the case of asheet shape) of preferably 1.5 mm or less, 1.3 mm or less, 1.1 mm orless, 0.8 mm or less, 0.6 mm or less, 0.5 mm or less, 0.3 mm or less,0.2 mm or less, particularly preferably 0.1 mm or less. As the thicknessof the glass becomes smaller, its flexibility increases, and alightingdevice with excellent design can be easily produced. However, when thethickness becomes extremely small, the glass is liable to be damaged.Thus, the thickness is preferably 10 μm or more, particularly preferably30 μm or more.

When the high refractive index glass of the second embodiment has asheet shape, the glass sheet preferably has an unpolished surface as atleast one surface (particular preferably has an entirely unpolished,effective surface as the effective surface in at least one surface). Thetheoretical strength of glass is intrinsically very high. However, glassoften breaks even by a stress far lower than the theoretical strength.This is because small defects called Griffith flaw are produced in thesurfaces of the glass in some steps after the glass is formed into aglass sheet, such as a polishing step. Thus, when a surface of glass isnot polished, the mechanical strength that the glass intrinsically hasis not easily impaired, and hence the glass does not easily break. Inaddition, the production cost of the glass sheet can be reduced, becausethe polishing step can be simplified or eliminated.

The high refractive index glass of the second embodiment comprises anunpolished surface having a surface roughness Ra of preferably 10 Å orless, 5 Å or less, 3 Å or less, particularly preferably 2 Å or less.When the surface roughness Ra is larger than 10 Å, the quality of atransparent conductive film formed on the surface deteriorates anduniform light emission is not easily achieved.

The high refractive index glass of the second embodiment is formedpreferably by a down-draw method, particularly preferably by an overflowdown-draw method. With this, an unpolished glass sheet having goodsurface quality can be produced. This is because, when a glass sheet isformed by the overflow down-draw method, the surfaces that should serveas the surfaces of the glass sheet are formed in the state of a freesurface without being brought into contact with a trough-shapedrefractory. The structure and material of the trough-shaped structureare not particularly limited as long as the desired size and surfaceprecision of the glass sheet can be achieved. Further, a method ofapplying a force to molten glass for down-drawing the molten glassdownward is not particularly limited, either. For example, it ispossible to adopt a method comprising rotating a heat-resistant rollhaving a sufficiently large width in the state of being in contact withmolten glass, to thereby draw the molten glass, or a method comprisingbringing a plurality of pairs of heat-resistant rolls into contact withonly the vicinity of the edge surfaces of molten glass, to thereby drawthe molten glass. Note that it is possible to adopt a slot down-drawmethod as the down-draw method, other than adopting the overflowdown-draw method. With this, a glass sheet having a small thickness canbe easily manufactured. Herein, the term “slot down-draw method” refersto a method of forming a glass sheet by down-drawing molten glassdownward while pouring the molten glass from apertures having asubstantially rectangular shape.

The high refractive index glass of the second embodiment is preferablyformed by a float method. With this, it is possible to produce largeglass sheets at low cost in large numbers.

A method other than the above-mentioned forming methods, such as are-draw method, a float method, or a roll-out method, may also beadopted.

The high refractive index glass of the second embodiment is preferablysubjected to roughening treatment on one of its surfaces by HF etching,sandblasting, or the like. The surface roughness Ra of the rougheningtreated surface is preferably 10 Å or more, 20 Å or more, 30 Å or more,particularly preferably 50 Å or more. When the roughening treatedsurface is arranged on the side to be brought into contact with air ofan OLED lighting device or the like, because the roughening treatedsurface has a non-reflective structure, light produced in an organiclight-emitting layer does not easily return into the organiclight-emitting layer. As a result, light extraction efficiency can beenhanced. Further, irregularities may be provided in a surface of glass(thermal processing such as re-pressing). With this, a precisereflective structure can be formed in the surface of the glass. Theinterval and depth of the irregularities are recommended to be adjustedin consideration of the refractive index nd of the glass. Further, aresin film with irregularities may be attached on a surface of glass.

Further, when atmospheric plasma processing is adopted for rougheningtreatment, while the surface condition of one surface of a glass sheetis maintained, the other surface of the glass sheet can be uniformlysubjected to the roughening treatment. Further, it is preferred to use agas containing F (such as SF₆ or CF₄) as a source for the atmosphericplasma processing. With this, a plasma containing an HF-based gas isgenerated, and hence the efficiency of the roughening treatment isenhanced.

Further, it is also preferred to adopt a method comprising formingirregularities in one surface at the time of forming glass into a glasssheet. In this case, no independent roughening treatment is required asa separate step, and hence the efficiency of the roughening treatmentapplied to the glass sheet improves.

Next, a method of producing the high refractive index glass of thesecond embodiment is exemplified. First, a glass batch is manufacturedby blending glass materials so that a desired glass composition isachieved. Subsequently, the glass batch is melted and fined, and is thenformed into a desired shape. After that, the resultant is processed intoa desired shape.

Example 3

Hereinafter, examples of the second invention are described in detail.Note that the following examples are merely for illustrative purposes.The second invention is by no means limited to the following examples.

Tables 5 to 12 show examples of the second invention (Sample Nos. 20 to55) and a comparative example (Sample No. 56).

TABLE 5 Example No. 20 No. 21 No. 22 No. 23 No. 24 Glass SiO₂ 45.0 50.040.0 40.0 45.0 composition B₂O₃ — — — 10.0 2.5 (wt %) Al₂O₃ 5.0 — 10.0 —2.5 CaO 5.9 5.9 5.9 5.9 5.9 SrO 10.9 10.9 10.9 10.9 10.9 BaO 26.2 26.226.2 26.2 26.2 TiO₂ 4.0 4.0 4.0 4.0 4.0 ZrO₂ 3.0 3.0 3.0 3.0 3.0Refractive index nd 1.629 1.623 1.634 1.641 1.631 λ = 587.6 nm Density[g/cm³] 3.36 3.33 3.39 3.39 3.36 Thermal expansion 74 75 73 77 75coefficient [×10⁻⁷/° C.] 30 to 380° C. Ps [° C.] 695 682 710 636 662 Ta[° C.] 738 724 754 670 703 Ts [° C.] 896 881 913 Not 855 evaluated 10⁴dPa · s [° C.] 1,107 1,098 1,119 958 1,057 10³ dPa · s [° C.] 1,2141,204 1,223 1,037 1,159 10^(2.5) dPa · s [° C.] 1,285 1,276 1,292 1,0911,227 10² dPa · s [° C.] 1,376 1,367 1,379 1,159 1,313 TL [° C.] 1,070Not Not 1,138 1,008 evaluated evaluated log₁₀ηTL [dPa · s] 4.5 Not NotNot 4.6 evaluated evaluated evaluated HCl Degree of ∘ ∘ ∘ ∘ ∘ resistancecorrosion Outer ∘ ∘ ∘ ∘ ∘ appearance

TABLE 6 Example No. 25 No. 26 No. 27 No. 28 No. 29 Glass SiO₂ 45.0 42.542.5 47.5 42.5 composition B₂O₃ 5.0 2.5 5.0 — — (wt %) Al₂O₃ — 5.0 2.52.5 7.5 CaO 5.9 5.9 5.9 5.9 5.9 SrO 10.9 10.9 10.9 10.9 10.9 BaO 26.226.2 26.2 26.2 26.2 TiO₂ 4.0 4.0 4.0 4.0 4.0 ZrO₂ 3.0 3.0 3.0 3.0 3.0Refractive index nd 1.632 1.634 1.635 1.627 1.632 λ = 587.6 nm Density[g/cm³] 3.35 3.36 3.37 3.34 3.37 Thermal expansion 76 75 75 75 74coefficient [×10⁻⁷/° C.] 30 to 380° C. Ps [° C.] 650 Not 648 687 702evaluated Ta [° C.] 687 Not 687 730 746 evaluated Ts [° C.] 825 Not 829890 904 evaluated 10⁴ dPa · s [° C.] 1,018 1,059 1,017 1,101 1,112 10³dPa · s [° C.] 1,110 1,160 1,111 1,209 1,218 10^(2.5) dPa · s [° C.]1,173 1,227 1,174 1,281 1,288 10² dPa · s [° C.] 1,252 1,311 1,254 1,3731,378 TL [° C.] Not 1,001 987 1,075 1,169 evaluated log₁₀ηTL [dPa · s]Not Not 4.4 4.3 3.4 evaluated evaluated HCl Degree of ∘ ∘ ∘ ∘ ∘resistance corrosion Outer ∘ ∘ ∘ ∘ ∘ appearance

TABLE 7 Example No. 30 No. 31 No. 32 No. 33 No. 34 Glass SiO₂ 40.0 40.037.5 40.0 40.0 composition B₂O₃ 2.5 5.0 5.0 5.0 5.0 (wt %) Al₂O₃ 7.5 5.07.5 5.0 5.0 MgO — — — 3.0 3.0 CaO 5.9 5.9 5.9 5.9 2.9 SrO 10.9 10.9 10.97.9 10.9 BaO 26.2 26.2 26.2 26.2 26.2 TiO₂ 4.0 4.0 4.0 4.0 4.0 ZrO₂ 3.03.0 3.0 3.0 3.0 SO₃ — — 0.01 0.01 — Cl — — — — 0.01 CeO₂ — — — 0.01 —Refractive index nd 1.635 1.636 1.637 1.634 1.632 λ = 587.6 nm Density[g/cm³] 3.38 3.38 3.39 3.34 3.37 Thermal expansion 74 75 74 73 72coefficient [×10⁻⁷/° C.] 30 to 380° C. Ps [° C.] 669 649 651 644 645 Ta[° C.] 711 687 690 683 684 Ts [° C.] 865 831 835 828 830 10⁴ dPa · s [°C.] 1,066 1,021 1,022 1,013 1,020 10³ dPa · s [° C.] 1,166 1,116 1,1161,104 1,116 10^(2.5) dPa · s [° C.] 1,232 1,179 1,178 1,165 1,181 10²dPa · s [° C.] 1,316 1,259 1,257 1,242 1,260 TL [° C.] 1,083 969 1,056987 954 log₁₀ηTL [dPa · s] 3.8 4.7 3.6 4.4 5.0 HCl Degree of ∘ ∘ ∘ ∘ ∘resistance corrosion Outer ∘ ∘ ∘ ∘ ∘ appearance

TABLE 8 Example No. 35 No. 36 No. 37 No. 38 No. 39 Glass SiO₂ 40.0 40.140.0 40.0 40.0 composition B₂O₃ 5.0 5.0 5.0 5.0 5.0 (wt %) Al₂O₃ 5.0 5.05.0 5.0 5.0 MgO 6.0 3.0 3.0 6.0 6.0 CaO 2.9 8.8 — 5.9 — SrO 7.9 4.9 13.84.9 10.8 BaO 26.2 26.2 26.2 26.2 26.2 TiO₂ 4.0 4.0 4.0 4.0 4.0 ZrO₂ 3.03.0 3.0 3.0 3.0 SnO₂ — 0.01 0.01 0.01 — SO₃ — 0.01 0.02 — — Cl 0.01 — —0.01 — CeO₂ — — — — 0.04 Refractive index nd 1.630 1.637 1.629 1.6331.628 λ = 587.6 nm Density [g/cm³] 3.32 3.31 3.39 3.29 3.35 Thermalexpansion 71 75 72 72 70 coefficient [×10⁻⁷/° C.] 30 to 380° C. Ps [°C.] 644 645 646 644 645 Ta [° C.] 683 683 685 682 684 Ts [° C.] 829 827832 826 830 10⁴ dPa · s [° C.] 1,014 1,006 1,028 1,008 1,022 10³ dPa · s[° C.] 1,106 1,095 1,127 1,096 1,118 10^(2.5) dPa · s [° C.] 1,168 1,1551,193 1,155 1,182 10² dPa · s [° C.] 1,245 1,229 1,277 1,230 1,261 TL [°C.] 967 1,026 983 Not 973 evaluated log₁₀ηTL [dPa · s] 4.7 3.7 4.6 Not4.7 evaluated HCl Degree of ∘ ∘ ∘ ∘ ∘ resistance corrosion Outer ∘ ∘ ∘ ∘∘ appearance

TABLE 9 Example No. 40 No. 41 No. 42 No. 43 No. 44 Glass SiO₂ 40.0 40.040.0 40.0 39.9 composition B₂O₃ 5.0 5.0 5.0 5.0 7.5 (wt %) Al₂O₃ 5.0 5.05.0 5.0 2.5 MgO 9.0 9.0 12.0 — — CaO 2.9 — — 2.9 5.9 SrO 4.9 7.8 4.810.9 10.9 BaO 26.2 26.2 26.2 26.2 26.2 TiO₂ 4.0 4.0 4.0 7.0 4.0 ZrO₂ 3.03.0 3.0 3.0 3.0 SnO₂ 0.01 0.01 0.01 0.01 0.005 SO₃ 0.01 — — — — Cl 0.010.01 — — 0.1 CeO₂ — — — — 0.005 Refractive index nd 1.629 1.627 1.6261.648 1.638 λ = 587.6 nm Density [g/cm³] 3.28 3.30 3.27 3.38 3.38Thermal expansion 70 70 69 71 75 coefficient [×10⁻⁷/° C.] 30 to 380° C.Ps [° C.] 646 647 650 654 640 Ta [° C.] 684 685 688 692 676 Ts [° C.]827 830 829 834 809 10⁴ dPa · s [° C.] 1,008 1,015 1,024 1,024 987 10³dPa · s [° C.] 1,097 1,106 1,112 1,122 1,076 10^(2.5) dPa · s [° C.]1,156 1,168 1,167 1,188 1,136 10² dPa · s [° C.] 1,230 1,245 1,229 1,2711,211 TL [° C.] Not Not Not 1,022 979 evaluated evaluated evaluatedlog₁₀ηTL [dPa · s] Not Not Not 4.0 4.1 evaluated evaluated evaluated HClDegree of ∘ ∘ ∘ ∘ ∘ resistance corrosion Outer ∘ ∘ ∘ ∘ ∘ appearance

TABLE 10 Example No. 45 No. 46 No. 47 No. 48 No. 49 Glass SiO₂ 37.5 42.437.5 39.6 39.7 composition B₂O₃ 7.5 7.5 10.0 5.0 5.0 (wt %) Al₂O₃ 5.0 —2.5 5.0 5.0 CaO 5.9 5.9 5.9 2.9 — SrO 10.9 10.9 10.9 13.9 16.8 BaO 26.226.2 26.2 26.2 26.2 TiO₂ 4.0 4.0 4.0 4.0 4.0 ZrO₂ 3.0 3.0 3.0 3.0 3.0SnO₂ 0.005 0.005 0.005 0.4 0.2 SO₃ 0.005 0.01 0.01 — 0.05 Cl 0.005 0.10.005 — — Refractive index nd 1.639 1.637 1.642 1.634 1.632 λ = 587.6 nmDensity [g/cm³] 3.39 3.38 3.39 3.36 3.34 Thermal expansion 76 75 76 7372 coefficient [×10⁻⁷/° C.] 30 to 380° C. Ps [° C.] 638 643 632 651 651Ta [° C.] 674 678 666 688 689 Ts [° C.] 808 807 792 834 836 10⁴ dPa · s[° C.] 987 993 956 1,025 1,033 10³ dPa · s [° C.] 1,075 1,077 1,0381,120 1,131 10^(2.5) dPa · s [° C.] 1,136 1,134 1,093 1,185 1,199 10²dPa · s [° C.] 1,211 1,207 1,162 1,268 1,285 TL [° C.] 952 Not 964 NotNot evaluated evaluated evaluated log₁₀ηTL [dPa · s] 4.5 Not 3.9 Not Notevaluated evaluated evaluated HCl Degree of ∘ ∘ ∘ ∘ ∘ resistancecorrosion Outer ∘ ∘ ∘ ∘ ∘ appearance

TABLE 11 Example No. 50 No. 51 No. 52 No. 53 No. 54 Glass SiO₂ 39.6 39.639.8 39.7 39.6 composition B₂O₃ 5.0 5.0 5.0 5.0 5.0 (wt %) Al₂O₃ 5.0 5.05.0 5.0 5.0 CaO 5.9 5.9 8.9 5.9 2.9 SrO 7.9 13.9 10.9 7.9 10.9 BaO 26.223.2 23.2 29.2 29.2 TiO₂ 7.0 4.0 4.0 4.0 4.0 ZrO₂ 3.0 3.0 3.0 3.0 3.0SnO₂ — 0.05 0.1 0.1 — SO₃ — — — — 0.3 Cl 0.2 0.3 0.1 0.1 0.05 CeO₂ 0.2 —0.005 0.1 — Refractive index nd 1.649 1.636 1.640 1.634 1.632 λ = 587.6nm Density [g/cm³] 3.34 3.39 3.37 3.37 3.39 Thermal expansion 72 76 7774 73 coefficient [×10⁻⁷/° C.] 30 to 380° C. Ps [° C.] 653 649 648 651652 Ta [° C.] 690 687 686 689 690 Ts [° C.] 830 829 828 835 836 10⁴ dPa· s [° C.] 1,010 1,011 1,003 1,023 1,031 10³ dPa · s [° C.] 1,101 1,1011,090 1,117 1,128 10^(2.5) dPa · s [° C.] 1,162 1,162 1,148 1,180 1,19410² dPa · s [° C.] 1,243 1,241 1,224 1,261 1,278 TL [° C.] Not Not NotNot Not evaluated evaluated evaluated evaluated evaluated log₁₀ηTL [dPa· s] Not Not Not Not Not evaluated evaluated evaluated evaluatedevaluated HCl Degree of ∘ ∘ ∘ ∘ ∘ resistance corrosion Outer ∘ ∘ ∘ ∘ ∘appearance

TABLE 12 Comparative Example Example No. 55 No. 56 Glass SiO₂ 39.8 2.5composition B₂O₃ 5.0 31.0 (wt %) Al₂O₃ 5.0 — CaO 3.9 — SrO 10.9 10 BaO26.2 — ZnO — 0.9 TiO₂ 4.0 — ZrO₂ 5.0 6.6 La₂O₃ — 46.0 Y₂O₃ — 11.0 Nb₂O₅— 1.0 SnO₂ 0.05 — SO₃ 0.05 — Cl 0.05 — CeO₂ — — Refractive index nd1.638 1.773 λ = 587.6 nm Density [g/cm³] 3.38 4.12 Thermal expansion 7172 coefficient [×10⁻⁷/° C.] 30 to 380° C. Ps [° C.] 659 635 Ta [° C.]698 658 Ts [° C.] 845 738 10⁴ dPa · s [° C.] 1,038 Not evaluated 10³ dPa· s [° C.] 1,134 Not evaluated 10^(2.5) dPa · s [° C.] 1,199 Notevaluated 10² dPa · s [° C.] 1,283 Not evaluated TL [° C.] Not Notevaluated evaluated log₁₀ηTL [dPa · s] Not Not evaluated evaluated HClDegree of ∘ x resistance corrosion Outer ∘ x appearance

First, glass materials were blended so that each glass compositiondescribed in Tables 5 to 12 was achieved. After that, the resultantglass batch was fed into a glass melting furnace and melted at 1,500° C.for 4 hours. Next, the resultant molten glass was poured on a carbonsheet to be formed into a glass sheet, followed by predeterminedannealing treatment. Finally, the resultant glass sheet was evaluatedfor its various characteristics.

The refractive index nd is a value obtained by producing samples havinga rectangular parallelepiped shape of 25 mm by 25 mm by about 3 mm, thensubjecting the samples to annealing treatment at a cooling rate of 0.1°C./min in the temperature range from (annealing point Ta+30° C.) to(strain point Ps-50° C.), and subsequently measuring the refractiveindex nd with a refractometer KPR-2000 manufactured by ShimadzuCorporation in a state in which an immersion liquid having a refractiveindex nd matching to that of the samples is immersed between two glasssamples.

The density is a value obtained by measurement using a well-knownArchimedes method.

The thermal expansion coefficient is a value obtained by measurement ofan average thermal expansion coefficient at 30 to 380° C. with adilatometer. A cylindrical sample (having end surfaces subjected to Rprocessing) having a size of 5 mm in diameter by 20 mm in length wasused as a measurement sample.

The strain point Ps is a value obtained by measurement based on a methodas described in ASTM C336-71. Note that, as the strain point Ps becomeshigher, the heat resistance becomes higher.

The annealing point Ta and the softening point Ts are values obtained bymeasurement based on a method as described in ASTM C338-93.

The temperatures at viscosities of 10^(4.0) dPa·s, 10^(3.0) dPa·s,10^(2.5) dPa·s, and 10^(2.0) dPa·s are values obtained by measurementusing a platinum sphere pull up method. Note that, as each of thetemperatures becomes lower, the meltability becomes more excellent.

The liquidus temperature TL is a value obtained by measuring atemperature at which crystals of glass deposit when glass powder thathas passed through a standard 30-mesh sieve (500 μm) and remained on a50-mesh sieve (300 μm) is placed in a platinum boat and kept in agradient heating furnace for 24 hours. Further, the liquidus viscositylog₁₀ηTL is a value obtained by measuring the viscosity of glass at itsliquidus temperature by a platinum sphere pull up method. Note that, asthe liquidus viscosity becomes higher and the liquidus temperaturebecomes lower, each of the denitrification resistance and theformability becomes more excellent.

The HCl resistance was evaluated according to the following method.First, both surfaces of each glass sample were subjected to opticalpolishing. After that, the both surfaces were partially masked and thensubjected to chemical treatment under the following condition. After thechemical treatment, the masks were removed and a surface roughness meterwas used to measure the height of a step formed by a masked portion anda corroded portion. The value obtained by the measurement was defined asthe “degree of corrosion.” The HCl resistance (degree of corrosion) wasevaluated on the basis of the following criteria. When the degree ofcorrosion was more than 20 μm, the corrosion was represented by Symbol“x”, and when the degree of corrosion was 20 μm or less, the corrosionwas represented by Symbol “∘”. The HCl resistance (outer appearance) wasevaluated on the basis of the following criteria. Both surfaces of eachglass sample were subjected to optical polishing, followed by chemicaltreatment under the following condition, and then, the both surfaces ofeach glass sample were visually observed. When a glass sample wascloudy, its surfaces were rough, or cracks were found in the glasssample, the outer appearance of the glass sample was represented bySymbol “x”, and when a glass sample remained unchanged, the outerappearance of the glass sample was represented by Symbol “∘”.

The treatment in evaluating the HCl resistance (degree of corrosion) wasperformed under the condition of immersing a glass sample in an aqueoussolution of 10 mass % HCl at 80° C. for 24 hours. The treatment inevaluating the HCl resistance (outer appearance) was performed under thecondition of immersing a glass sample in an aqueous solution of 10 mass% HCl at 80° C. for 24 hours.

As clear from the tables, each of Sample Nos. 20 to 55 weresubstantially free of alkali components and rare metal oxides, had arefractive index nd of 1.623 or more, and had good acid resistance.Further, each of Sample Nos. 20, 24, 27 to 37, 39, 43 to 45, and 47 to55 had a liquidus viscosity of 10^(3.4) dPa·s or more. Further, each ofSample Nos. 20 to 31 had a low density even though having a highrefractive index nd, and hence they can be used for reducing the weightof a device. In addition, each of Sample Nos. 20 to 31 had a thermalexpansion coefficient approximating that of a transparent conductivefilm, and hence it is expected that the warpage of a glass sheetproduced by using any of the samples can be suppressed. Further, each ofSample Nos. 20 to 25 and 27 to 55 had a high strain point, and hence itis presumed that the thermal shrinkage of the glass can be suppressed inthe production process of a device. On the other hand, Sample No. 56comprised rare metal oxides in a large amount in its glass composition,and hence had a high density and low acid resistance.

INDUSTRIAL APPLICABILITY

The high refractive index glass of the present invention has arefractive index nd of 1.55 or more and has a high liquidus viscosity.Further, the high refractive index glass of the present invention can beproduced by excluding rare metal oxides from its glass composition fromthe viewpoint of reducing the cost of materials, and can also beproduced by excluding As₂O₃, Sb₂O₃, and the like from its glasscomposition from the environmental viewpoint. Therefore, the highrefractive index glass of the present invention is suitable for asubstrate for an OLED device, in particular, a substrate for an OLEDlighting device. Note that the high refractive index glass of thepresent invention can also be used as, for example, a substrate for aflat panel display such as a liquid crystal display, a cover glass foran image sensor such as a charge coupled device (CCD) or a contact imagesensor (CIS), and a substrate for a solar cell.

The invention claimed is:
 1. A high refractive index glass, comprising,as a glass composition in terms of mass %, 35 to 50% of SiO₂, 0 to 1.5%of Li₂O+Na₂O+K₂O, 0.1 to 35% of SrO, 0 to 35% of BaO, 0.001 to 25% ofTiO₂, 0 to 3% of B₂O₃, and 0 to 9% of La₂O₃+Nb₂O₅+Gd₂O₃, and having arefractive index nd of 1.55 to 2.3.
 2. The high refractive index glassaccording to claim 1, further comprising 0 to 3 mass % of MgO.
 3. Thehigh refractive index glass according to claim 1, further comprising 1to 20 mass % of ZrO₂+TiO₂.
 4. The high refractive index glass accordingto claim 1, wherein the high refractive index glass has a sheet shape.5. The high refractive index glass according to claim 1, wherein thehigh refractive index glass has a liquidus viscosity of 10^(3.0) dPa·sor more.
 6. The high refractive index glass according to claim 1,wherein the high refractive index glass is formed by a float method or adown-draw method.